Prematurity is the term used for babies born before they are classed as 'full term'.
You might also hear it referred to as pre-term, and the babies who are born prematurely are sometimes called 'preemies'.
Premature births can happen for many reasons, sometimes we know the reason and other times we don't. It can be hard to not focus on WHY your baby was born prematurely if you don't know, and as a parent you often feel guilty (especially if you were carrying the baby) , even if you know the reason why!

Premature babies are often split into categories:
22+0-27+6 weeks gestation (born weighing under 800g). At the smallest side of prematurity you have 'micro-preemies' or 'extremely premature infants'.
28+0-31+6 weeks gestation. You then have 'very premature infants'.
32+0-33+6 weeks gestation. These babies are 'moderately premature infants'.
34+0 -36.6 weeks gestation, known as 'late premature infants'.