A B_CALL generally runs a short program within the OS. While typically attributed to beginning programmers, it can still be useful in memory conservation.
Should be understandable. Clears the whole LCD.
In case you memorized the hex code, the code is undocumented, or you are typing directly on the calculator. For example, B_CALL(_ClrLCDFull) would be EF4045.
Preferred method for on computer. The system routine name generally does what it says it does.
2 byte hex number
This is the memory in the jump table. See LUTs and Jump Tables.
Or you can put the name defined in the include file (ti83plus.inc). Whatever you prefer, and as long as you (or readers) can understand it.
Besides running the system routines, B_CALLs are also used in Application programming. See Applications.