A priori is a French expression which comes from Latin and means “at first glance”, “at first sight”, “in principle” and “should”.

Example sentences
This first sentence could start with at first glance, at first sight or in principle.
A priori, c’est une bonne idée !
That seems like a good ideal.
A priori, la fête commence vers 19h.
The party should start around 7pm.
This sentence was a bit hard to translate. The literal translation of il faut is “it’s necessary”. In the negation it can translate to “don’t” or “you shouldn’t”. This sentence could have also ended with sans consideration (without consideration).
Il ne faut pas accepter son offre a priori.
You shouldn’t accept his offer at first glance.
Où vas-tu pour Noël ? – A priori, je vais faire du ski en Italie.
Where are you going for Christmas? – In principle, I should be going to Italy to ski.
Expression origin
According to britannica.com, a priori in epistemology (the theory of knowledge) is “knowledge that is independent of all particular experiences”. The expression exists in English but is used much more often in French. Note that a priori is correct. There is no grave accent on a. Hence, à priori would be incorrect.