Licence
A licence is the permission that says how you may use something that someone else made.
In a simple example
A picture or a font comes with a licence: some may be used in a shop, some only for personal use.
Why it matters to you
Using something without the right licence can lead to a demand for money or a takedown.
Do not confuse with
Free to download does not always mean free to use for business. Read the licence.