To make the shell interpret a metacharacter literally:
echo & [1] 1463 [1] Done echo echo \& &
The shell interprets the & character at the end of a command line to mean that the command is to be run in the background. So the command echo & simply runs the echo command in the background and since the command has nothing to echo it immediately exits.
When the & character is preceded by a \ (backslash) the echo command interprets this literally and simply echoes (displays) this character on the screen.