Investment Banking is the raising of funds, both in debt and equity, and the division handling this in an investment bank is often called the "Investment Banking Division" (IBD). However, only a few small firms solely provide this service. Almost all investment banks are heavily involved in providing additional financial services for clients, such as the trading of fixed income, foreign exchange, commodity, and equity securities. It is therefore acceptable to refer to both the "Investment Banking Division" and other 'front office' divisions such as "Fixed Income" as part of "investment banking," and any employee involved in either side as an "investment banker." Furthermore, one who engages in these activities in-house at a non-investment bank is also considered an investment banker. That said, many if not most IBD employees consider the title of Investment Banker reserved to them alone and bristle at self-referential use of this title by employees of other IB divisions, especially those engaged in Sales & Trading.
More commonly used today to characterize what was traditionally termed "investment banking" is "sell side." This is trading securities for cash or securities (i.e., facilitating transactions, market-making), or the promotion of securities (i.e. underwriting, research, etc.).
The "buy side" constitutes the pension funds, mutual funds, hedge funds, and the investing public who consume the products and services of the sell-side in order to maximize their return on investment. Many firms have both buy and sell side components.
Generally speaking, those on the sell side are engaged in persuading those on the buy side. As such, it is sometimes considered to be more desirable to be on the buy side, since discretionary control over decisions lies with them. This said, it is not necessarily the case that the buy side is more personally lucrative than the sell side. As with most other endeavors, financial rewards await those who through luck or skill identify opportunity, regardless of whether they are selling or buying.