Maybe is an adverb that means perhaps. It is a single word. Maybe also has its place as a noun, meaning an event or situation that’s not for certain—again spelled as one word.
May be is a two-word verb phrase that means something may or may not happen or something does or does not have a particular characteristic.
Maybe and may be are not interchangeable, even though they sound exactly the same. Consider these examples:
Maybe I’ll see you tomorrow.
Donnie’s cat was maybe eight to nine pounds overweight.
Maybe Stan has a good reason for being late.