An apéro is a term derived from the word "apéritif" and refers to the time before dinner when you enjoy a glass of a mostly alcoholic drink and a few snacks alone or with others.
Example: It is 7 p.m. It is time for an apéro.
Traditionally, aperitifs are served in Europe in bars or restaurants in the late afternoon or early evening.
Overall, the aperitif is intended to help you enjoy your meal and make the evening pleasant in good company.