What does the symbol "::" mean in computer science? What does the symbol $::$ mean in the following statement?

$\forall{x}\in K :: x \longrightarrow x$

A cycle in a graph is a path that starts and ends on the same node.
Clearly, if nodes in K lie on a cycle, then $\forall{x}\in K :: x \longrightarrow x$.

Look at page 56 in the following.

https://books.google.co.in/books?id=nel4vdeLcqkC&amp;pg=PR7&amp;source=gbs_selected_pages&amp;cad=2#v=onepage&amp;q&amp;f=false
It is a delimiter between to parts of expression. You can think of it as notation for the English phrase 'such that'.
Read your formula as $`` \forall x\in K \text{ such that } x \longrightarrow x"$.