Baffling MySQL data types

[admin]

This is a bit of a newbie question.

I am curious as to the differnece between :

TEXT
and
TEXT(150)

I understand that the 150 is providing a rough estimate of size but does leaving out the size default the size to 0. Is size in this case measured in characers? Is it more expensive to do things this way??

Thanks for the help.

Mayu