task

This word is often used as shorthand in the (*cough* poorly written *cough*) LSL documentation and basically refers to either:

The object this script is running on, the script itself, the object's script that called the function, or the object containing the script calling the function. (The latter is the most likely definition.)

It's used like this:

llGetInventoryNumber(integer INVENTORY_CONSTANT); returns the number of inventory items contained in task.
or:
llGetNumberOfSides(); returns the task's number of sides.