In Spanish we refer to tilde diacrítica when we use an acute accent in a word to differentiate it from another word that is written exactly the same way but has a different meaning.
Examples of words with tilde diacrítica are:
tú vs tu (subject pronoun vs possessive adjective)
Tú eres inteligente.You are intelligent. ("You" singular informal)
Soy tu madre.I am your mum. ("Your" singular informal)
mí vs mi (pronoun vs possessive adjective)
A mí me gusta mucho el pescado a la plancha.I really like grilled fish. (Lit: grilled fish is pleasing to me)
Mi abuelo no tiene dientes.My grandad has no teeth.
más vs mas (adverb vs conjunction)
Pedro siempre ha sido más generoso que su hermano.Pedro has always been more generous than his brother.
Yo les ofrecí mi ayuda mas no quisieron aceptarla.I offered them my help nevertheless they refused to accept it.
Other words with tildes diacríticas are aún/aun, sí/si, té/te, dé/de, and él/el.