Investment banking means businesses creating capital for others. More specifically, "investment banking" speaks to the branch of banking in which organizations act as "financial intermediaries." This includes being underwriters or agents for other companies or individuals, where the banker issues securities on their behalf. They also advise these other companies (or clients) on the best possible decisions when dealing with stocks; both in terms of issuing and placement.
In essence, these bankers are responsible for pairing traders, or lenders and borrowers. The aim of investment bankers is to make their clients money regardless of the state of the economy, which means they must know how to identify lucrative investments in any market. They must also find ways make the system work in the clients' favors, or at least avoid losses on their clients' side of the transaction.
This banking division also takes into consideration mergers, corporate reorganizations outside of mergers, brokerage for companies and individuals, and personal trading.