To fail to remember information, tasks, or objects.
Encoding Strategies:
linguistic

oblivious
not aware of
+
-ar
verb suffix
Olvidar means to forget and is a verb1 related to the English word oblivious0, since an oblivious person doesn't pay attention or remember things.
olvidar
to forget
To fail to remember something.
- Olvidé mi cartera = I forgot my wallet
- Olvidé tu cumpleaños y lo siento = I forgot your birthday and I'm sorry
olvidarse
to forget (personal emphasis)
The reflexive form emphasizes the person doing the forgetting.
- Me olvidé mi cartera = I forgot my wallet (I myself forgot my wallet)
- Me olvidé el paraguas en casa = I forgot my umbrella at home
to forget, to get forgotten (to slip one's mind)
The thing being forgotten 'forgets itself,' and this forgetting is directed towards someone.
- Se me olvidó la cartera = I forgot my wallet (the wallet gets forgotten by me)
- Se me olvidaron las llaves = I forgot my keys (my keys got forgotten by me)
olvidarse de
to forget about (emphasizes source)
The 'de' signifies the source of the forgetting, the thing you are forgetting about.
- Me olvidé de la fiesta = I forgot about the party
- Me olvidé de comprar pan = I forgot to buy bread (I forgot about buying bread)