What is a stock warrant? How do warrants work? I've been told they are similar to options; how? Then why not just call them options - what makes them different?
In general, a warrant is a security issued by a company allowing the holder to purchase a certain number of a particular class of shares at a certain price for a particular period of time. They differ from exchange traded options (i.e. calls and puts) in that they are issued by the company that issued the underlying shares that they allow you to purchase whereas calls and puts are generally written by other investors.
The other big difference between options and warrants is that options are standardized. Any call or put you buy on a particular exchange has basically the same set of rules governing use. By contrast, a warrant may have all kinds of stipulations that must occur before you can execute, such as price events (e.g. only if the stock hits a certain price) or business events (e.g. only if the company elects to defer payment on a bond issued at the same time as the warrant).
Warrants are generally a bad choice for small and inexperienced investors since each warrant issue is different and you often need a lawyer or other qualified professional to fully understand all to possible outcomes.
In Australia there are 2 type of warrants (I don't know if it is the same in the US, UK and other countries), the first are trading warrants and the second are instalment warrants.
The trading warrants are exactly what it says, they are used for trading. They are similar to option and have calls and puts. As Cameron says, they differ from exchange traded options in that they are issued by the financial companies whereas options are generally written by other investors.
Instalment warrants on the other hand are usually bought and sold by investors with a longer term view. There are no calls and puts and you can just go long with them. They are also issued by financial companies, and how they work is best explained through an example: if I was to buy a stock directly say I would be paying $50 per share, however an instalment warrant in the underlying stock may be offered for $27 per warrant. I could buy the warrant directly from the company when it is issued or on the secondary market just like shares. I would pay the $27 per warrant upfront, and then in 2 years time when the warrant expires I have the choice to purchase the underlying stock for the strike price of say $28, roll over to a new issue of warrants, sell it back on the secondary market, or let it expire, in which case I would receive any intrinsic value left in the warrant.
You would have noticed that the warrant purchase price plus the strike price adds up to more than the share price ($55 compared to $50). This is the interest component inherent in the warrant which covers the borrowing costs until expiry, when you pay the second portion (the strike price) and receive the underlying shares.
Another difference between Instalment warrants and trading warrants (and options) is that with instalment warrants you still get the full dividends just like the shares, but at a higher yield than the shares.