Examples:
"We Will Rock You" and "We Are The Champions" by Queen
"Load Out" and "Stay" by Jackson Browne
Examples:
"We Will Rock You" and "We Are The Champions" by Queen
"Load Out" and "Stay" by Jackson Browne
There's not a specific term per se, but you might hear such songs referred to as a "common pairing" — not formal in any sense, but frequently used.
If the songs are combined such that they form, in effect, one longer song, it's a "medley". In a medley the songs come one after they other; whereas, in a "mashup" they could be consecutive, simultaneous, interleaved, or a combination thereof.
The transition between two songs in called a "segue". This can be musical, but also could be extra-musical (e.g., talking).
A suite is a set of pieces of music that belong together, and are usually played in sequence.
That's mostly used for classical/‘serious’ music (and music originally written for movies/plays), where it usually refers to instrumental pieces; the vocal equivalent would probably be song cycle.
However, modern artists including Steve Hillage, Prince, Synergy, Sonny Rollins, and Mike Batt have included suites on their albums — of songs as well as instrumentals.
Quick answer
The term used to describe two songs usually sung together is polyphony. In music, the simultaneous combination of two or more tones or melodic lines (the term derives from the Greek word for “many sounds”). Thus, even a single interval made up of two simultaneous tones or a chord of three simultaneous tones is rudimentarily polyphonic. (“Polyphony | Definition, Melodic Lines, & Counterpoint | Britannica”) Table of Contents show What is it called when you combine 2 songs?