A wrap is a very important concept in many TypoScript objects. A "wrap" is a text string, which is explode (split in parts) by "|" (the vertical line, ALT+0124).

So this is a wrap:

<B>  |  </B>

And if the string "World" is being wrapped by the wrap, the result is this:

<B>WORLD</B>

Notice that even though there are spaces between the wrap-parts and the divider ("|"), each wrap part is trimmed (trimming is to remove "whitespace" before and after something. "Whitespace" is space, tab and linebreak characters)

As you might have realized this is very, very useful because HTML is all about wrapping things into HTML-tags. And in this way, it's very easy to control and cope with.

(BTW: Wrap is listed as a Data type in the TSref)