rip is a flow of water out to sea
Every year 20 00 people are rescued and at least 20 people drown in rip related scenarios around the United Kingdom. The deadly nature of rip currents doesn't come from rips themselves - but lack of knowledge:
Never swim against the current.
A rip current is a narrow channel of water that can flow hundreds of metres out to sea (that's way beyond the surf zone). As water surges up the beach with a breaking wave, it flows along the shoreline until it finds the path of least resistance back to sea. These paths of least resistance can be headlands, cliffs, reefs or gaps in beach sand banks. Once the water finds these paths, it will flow back to sea at speeds of up to 2.5 metres per second. That's over 100 metres in a minute.
For surfers, rips are a fantastic way of getting out back (beyond breaking waves) quickly and effortlessly. For those who are unaware or unsuspected, they can be quickly dragged out to where they don't want to be. Without a basic understanding of rip currents, most people in this situation would immediately start swimming back to shore - but not even gold medallists can keep that up; and so most deaths occur because people have been swimming against the rip, without going anywhere, and tiring to the point of exhaustion.