OCR stands for Optical Character Recognition. It's the technology that looks at a picture of text — a photo, a screenshot, or a scanned page — and figures out the actual letters and words, giving you real text you can copy, search and edit.
Without OCR, a scanned document is just an image: you can see the words but you can't select or search them. OCR adds a hidden (or extracted) text layer so the content becomes usable.
Common uses include digitising printed documents, making scanned PDFs searchable, and pulling text out of a photo.
You can OCR a scan with OCR PDF or extract text from a picture with Image to Text.