What is a secondary stock offering? Well, also called a “follow-on offering” is similar in may ways to an IPO, or “initial public offering.” The only difference that an IPO is how a fledgling company can raise capital by offering stock for the first time — while a secondary offering is the sale of shares by an existing company that wishes to refinance or raise capital for growth. Follow-on offerings can also moves by majority shareholders to exit their position by selling a large portion of stock.

More importantly, why should you care about secondary offerings? Well, many investors consider follow-on stock offerings bad news. In the first case, when a company issues more and increases outstanding stock, it spreads its value across a larger number of shares and thus decreases their value. In the second case when a large shareholder bails out, that could be a bearish sign — or could naturally deflate share prices since all the stock is being dumped at once instead of at market prices over a longer period.

However, not all secondary stock offerings are poorly received. For instance, recently Prudential Financial (NYSE: PRU) funded the acquisition of some American International Group (NYSE: AIG) business through a secondary offering. Also, some companies structured as partnerships or REITs under SEC rules often can only finance big moves via secondary offerings since by their nature they cannot sit on big cash reserves and keep favorable tax status.

Here’s a look at 11 big secondary offerings of note that have taken place recently:

Perhaps the most interesting secondary stock offering is that of mall owner General Growth Properties (NYSE: GGP). It  will raise $700 million with a secondary offering of 155 million new shares at around $14.75 a piece. The offering is part of a so-called “clawback” option on $6.8 billion pledged to General Growth by five big investors, led by Brookfield Asset Management (NYSE: BAM). Under recapitalization terms as the company emerged from bankruptcy and went public this spring, General Growth had the right to claw back and sell a portion of the shares if it could get better than $10 per share. Since GGP soared immediately after its IPO earlier in the year and stayed there, the move makes sense. General Growth will raise roughly $2.3 billion in selling all 155 million shares — $1.6 billion to replace the cash owed investors, and an additional $700 million surplus due to a wise deal made this spring.

Plains All American Pipeline (NYSE: PAA) on Friday sold a total of 4.2 million shares common at $62.60 per common unit, raising about $260 million after expenses. Despite taking a hit after the secondary offering was announced, PAA stock has enjoyed 18% returns so far in 2010 — and with a 6.1% dividend yield, the stock has been a favorite among income investors. Plains All American plans to use the cash to reduce outstanding borrowings, particularly related to recent costs of its Nexen Holdings acquisition.

Navios Maritime (NYSE: NNA) took a dive this week, shedding 13% on the heels of announcing a secondary offering of 6.5 million shares at around $5.50. The Greek-based tanker operator is off about 50% year-to-date after a brutal selloff in May. The company said the cash will be used for “general corporate purchases,” but the likely use could be the recently announced purchase of two new LR1 tankers for $82.8 million.

Clinical Data (NASDAQ: CLDA) recently announced plans to periodically sell up to $200 million of common and preferred stock as well as debt securities and warrants. The maker of central nervous system and cardiovascular therapeutics saw shares consolidate and move lower 5% last week as a result, and is about flat year-to-date.

Prudential Financial (NYSE:PRU) has raised close to $1 billion in a 18.35 million-share secondary offering recently. Proceeds will fund acquisitions of AIG Star Life Insurance and AIG Edison Life Insurance from bailed out American International Group (NYSE: AIG). In other words, all that cash is going to Uncle Sam as AIG spins off operations to pay back taxpayers. Prudential is up about 8% YTD, which is comparable to the broader market, but shares have lagged lately and have seen trouble moving higher since August. Looking forward, the acquisition may pay off for

DCP Midstream Partners (NYSE: DPM) has priced its public secondary offering of 2.5 million common shares at $34.96 per unit, with gross proceeds of close to $87 million. The partnership said it will use the cash for a previously announced acquisition of a 33% stake in DCP Southeast Texas business. However, the secondary stock offering is not contingent upon the consummation of the acquisition. DCP stock is up 18% year-to-date and yield a hefty 7.0% dividend.

Yet another partnership offering up stock, Enbridge Energy Partners (NYSE: EEP) has priced a public secondary offering of 5.2 million shares at $60.12 per unit, raising more than $300 million. Enbridge said the cash will mostly pay back outstanding debt used to acquire Elk City Gathering and Processing. EEP stock is up 13% year to date, and has a dividend yield of 6.7%.

Chimera Investment NYSE: CIM) is a real estate investment trust, or REIT, that recently sold 125 million shares at $3.85 per share to raise about $480 million. Chimera said the cash will purchase residential and commercial paper including mortgage-backed securities, prime and Alt-A mortgage loans, commercial mortgages, and so on. Shares have been volatile year-to-date, but are mostly flat. If the move pays off Chimera could reap rewards in 2011.

Invesco (NYSE: IVZ) announced a secondary offering of the approximately 30.9 million shares last week, which have been in the possession of Morgan Stanley (NYSE: MS) since June as part of a deal regarding its retail asset management business. MS declined to say when the offering would be completed, but the longer the company waits the longer it appears the shares may garner. IVZ stock is up about 20% in the last three months.

BlackRock (NYSE: BLK) announced recently it has completed the secondary offering of 58.7 million common stock shares — almost 44 million of those divested by Bank of America (NYSE: BAC) at $163. Blackrock shares have been under pressure in 2010, losing over 20% since the first of the year.

TRW Automotive  (NYSE: TRW), the world’s biggest supplier of vehicle-safety equipment, announced recently it will sell about 10 million shares of stock. Shares briefly tumbled almost 10% but have been slowly coming back. Besides, TRW is sitting on a gain of 31% year-to-date, despite the rollback. The sale is simply a divestiture by the Blackstone Group (NYSE: BX), which held 24% of outstanding TRW shares as of October. It first got its stake in 2002 when it acquired the company from Northrop Grumman (NYSE: NOC).

Jeff Reeves is editor of InvestorPlace.com. As of this writing, he did not own a position in any of the stocks named here. Follow Jeff on Twitter at http://twitter.com/JeffReevesIP.