What is foley?

Using YouTube I found a video which explained what foley was and how it is done in films. The link to the video is here(https://www.youtube.com/watch?v=sOOusLtr6NQ&feature=youtu.be)

From my research I learnt that foley is used a lot as it can be more effective than sound effects as the noises can be made in time with the image, where as using normal sound effects can be more time consuming by having to insert small clips and noises where they happen on screen.