What is an aperitif?
Apéritif is a French word, which, like its Italian counterpart, aperitivo, comes from the Latin aperire, meaning “to open". It is commonly shortened to apéro in casual conversations.
For an important part of France's, Italy's, and other European countries' dining traditions, aperitifs are a mix of fine food with alcoholic/soft beverages enjoyed just before a meal to whet the appetite.1 For instance, fingers food includes crackers, bread, cheese with chutney or honey, cured meat or olives. It should leave you fulfilled and content. Not hungry, yet not stuffed either.
The Apéritif moment is considered as being a perfect, convivial and informal pre-dinner time to relax and socialise with colleagues, partners and relatives - a real friendly ritual!

1. Source: www.thekitchn.com ; www.french-property.com.