DOMS stands for delayed onset muscle soreness.

This is muscle pain that begins after you’ve worked out – some people feel it the very next day and a lot of people seem to find it comes two days later. The soreness is perceived as a dull, aching pain in the affected muscle, often combined with tenderness and stiffness.

You can get DOMS from any form of exercise. It usually comes about if the body is not used to doing something or you have exerted yourself by increasing the load or increasing distance, for example. The body will respond to what it is not used to, and it will then adapt if you continue to do the same exercise after this.

High-intensity training can cause tiny, microscopic tears in your muscle fibres. Your body responds to this damage by increasing inflammation.

Eccentric exercise (tensing a muscle at the same time you lengthen it) can cause DOMs due to the breakdown of muscle tissue. As muscle fibres are repairing they can become knotted and reduce muscle elasticity.

You can still exercise with DOMs, however, you will feel discomfort. It is best to rest or rest that specific area/avoid that same activity; do something different and go back to that when you no longer feel pain. It can be good to still do something gentle such as walking to ease any stiffness.

Massage, foam rolling and stretching can all help to alleviate discomfort. Heat or ice can also reduce DOMS.

References:
https://www.healthline.com/health/doms#should-you-rest

https://en.wikipedia.org/wiki/Delayed_onset_muscle_soreness