Bash builtin commands (also known as "internal command") are part of the shell itself. Each builtin command is executed directly in the shell itself, instead of an external programme which the bash would load and run. For example, the top is an external command, and an alias is an internal or builtin command.
How do I find out if given command is an internal builtin or external?
type -a command-name-here command -V command-name-here ## find out if top is an internal builtin or an external command ## type -a top
top is /usr/bin/top
type -a alias
alias is a shell builtin
The bash executes the alias command directly as it is a shell builtin. Try following examples:
command -V ls type -a ls commamd -V date type -a date type -a vim command -V vim type -a firefox command -V firefox
A typical output: