From Facebook Developers Wiki

These are the parameter types that are used in API calls and FBML tags. These are all normally sent as "strings" anyway, but allow you to know what kind of data to put for the parameter.

Contents 1 array 2 bool 3 data 4 float 5 int 6 JSON array 7 markup 8 string

[edit] array

An array of values, usually separated by commas.

[edit] bool

A boolean, specified as true or false, yes or no, or number≠0 or 0.

[edit] data

Raw data. Currently used in the photos.upload API method to transmit the raw image data of the photo being uploaded.

[edit] float

A float. Currently used for specifying the weight of an fb:random-option, the version number in fb:fbml, and for the coordinates of a photo tag in the photo_tag FQL table.

[edit] int

An integer. Usually used for IDs of various types.

[edit] JSON array

An array of values in JSON format. For example, ['val1','val2','val3'].

[edit] markup

FBML markup.

[edit] string

Text.