Plain Vanilla

Regular. Normal. Typical. Boring. Think: white bread, suburban malls, network TV, in bed by 10, missionary position. No whipped cream. No sprinkles. No flavor. Plain vanilla.

In financial terms, it refers to the standard version of any financial product. Things like options and swaps can come in lots of exotic varieties. But these all play off of a conventional structure. That conventional structure is known as the "plain vanilla" form.