BSF = British Standard Fine
BSW = British Standard Whitworth.
BSP = British Standard Pipe
BA = British Association
UNF = Unified National Fine
UNC = Unified National Coarse
UNEF = Unified National Extra Fine.
NTP = National Taper Pipe
Whitworth form (and BSF and BSP  
threads are 55 degree while Unified form are 60 degree angle. BA form are 47.5 degree angle. Metric are 60 degree form.
BSW and UNC thread pitches are often the same, as are many BSF and UNF, but DO check! BSP and NTP are different thread form, and the TPI varies as well.
Metric threads are defined by diameter and pitch, so that you can have the standard Metric Coarse, say 12 x 1.75 and a fine version as 12 x1.5 or even finer at 12 x 1.25.
There is no reason why diameter and pitch cannot be non standard. Some Myford lathes used 7/8 x 12 tpi, while then later ones used 1 1/8 x 12 tpi. This is quite common practice for screw fitting chucks for lathes.
Allen Socket Head screws are often referred to as Capscrews. Csk signifies Countersunk head.And then there are Button head and Dome head varieties as well!
HTH
Howard