The words hadith, sunnah, isnad and matn.
A hadith is a report of something the Prophet Muhammad (peace and blessings be upon him) said, did or approved of, or a description of him. The Sunnah is his way as a whole: what those reports, taken together, teach us about how he lived and what he taught.
Every hadith has two parts:
When you open a hadith on this site you will see the text in Arabic and English, the Companion who narrated it, and the book it was taken from. That last line matters: a hadith is only as reliable as its source, so always note where it comes from.