A common abbreviation of system call in Unixland. Syscalls are means by which an application can call a function in kernelspace. While unavoidable, as under Unix they are the way programs do I/O, file system operations, memory allocation, and just about all other tasks, developers of good code try to minimize the number of them invoked. This is because a syscall causes a context switch, which can be expensive when syscalls are abused.