What is meant by "buy-side" and/or "sell-side"?

There is much confusion around these two terms but I figured WallStreetOasis would try to take a stab at how we think of "Buy-Side" and "Sell-Side."

A sell-side engagement for an Investment Bank means they are were hired to help sell a company or division. The opposite is true for the buy-side.

Oftentimes, ALL of investment banking in general, however is referred to "Sell-Side" work while industries like private equity, mutual funds, hedge funds, etc are referred to as "Buy-Side" industries. The rationale is that even if an Investment Bank is hired for a buy-side engagement, they still are selling their advisory services to that specific company. On the other hand a private equity fund (for example) is putting their own capital at risk (or their own investors) in a given transaction by actually going out and buying a company.

This gets more complicated in the Bulge Brackets where "Sell-Side" and "Buy-Side" are under one roof and can sometimes overlap. [further clarification / argument is welcome at wallstreetoasis@wallstreetoasis.com -- if you explain it better, we'll put your explanation up]