Catnapping is the name for very short naps, often around 30 to 45 minutes, where a baby wakes after a single sleep cycle instead of joining cycles into a longer nap. To a parent it can feel like the baby is up again the moment they went down.
In the early months it is common and usually developmentally normal. Babies' sleep is still maturing, and many start to link cycles and take longer naps as they get older, without much intervention.
Where you have some influence is timing. Offering the nap on an age-appropriate wake window, before the baby tips into overtired, and in a calm dim space, gives the best shot at a longer sleep. With twins, keeping their naps matched at least means two short naps happen together rather than eating the whole day between them.