What is %20 in google search URL?

In ASCII values, %20 refers to a space between 2 words. Suppose you searched," Hey google, whats the weather today?". Here there are 5 speces means the link will be like:
hey%20google+,%20whats%20the%20weather%20today+?
Now google has upgraded there url system and replaced %20 with +. Still many search engines still uses this feature.