These are two different forms of immigration status for which UK-resident EU citizens can apply under Appendix EU. However, which of these statuses any given one of these citizens is eligible for would depend on how long they have lived continuously in the UK.
Affected persons who have done so for over five years can apply for settled status, while those who haven’t would instead only be able to apply for pre-settled status. In this context, the word ‘continuously’ usually means not having been absent from the UK for over six months at a time.
However, you could remain entitled to settled status if, while a UK resident, you were absent for up to 12 months for an important reason – like pregnancy, childbirth, serious illness, study or vocational training. Another exemption would be if you undertook compulsory military service outside the UK for any period exceeding six months.