Word (data type)
When referring to a data type, the term word usually means the unit of data storage that some computer can most efficiently manipulate. For an "X-bit" computer, a word would most likely be X bits in size.
The term is very common in old file format specifications, where it's often not fully defined in that document. But it's a good bet that it means an unsigned 16-bit integer (though you'll still have to figure out its endianness).