Questions & Answers about Un billete de ida y vuelta.
Because billete is a masculine noun in Spanish, so it takes the masculine indefinite article un.
- un billete = a ticket
- una entrada = a ticket/admission ticket, but entrada is feminine
You usually have to learn the gender of each noun as part of the word.
In this sentence, billete means a ticket, especially for transport such as trains, buses, or planes.
In Spain, billete is the normal word for a travel ticket. In some Latin American countries, you may also hear boleto or other regional words.
Also note that billete can mean banknote in other contexts, so the exact meaning depends on the situation.