record 

An arbitrary sequence of bytes in a file. The UNIX operating system supports no record structure. Programs that use the files can impose any arbitrary record structure.  

cooperating processes

Two or more processes using some mechanism to regulate access to a shared resource. 

read lock

Lets other processes also apply a read lock and/or perform reads, and blocks other processes from writing or applying a write lock. 

write lock

Blocks all other process from reading, writing, or applying any lock.  

advisory lock

Returns an error without blocking to a process that does not hold the lock. Advisory locking is not enforced on creat(2), open(2), read(2), or write(2) operations.

mandatory lock

Blocks execution of processes that do not hold the lock. Access to locked records is enforced on creat(2), open(2), read(2), and write(2) operations.