There are two possible definitions for Secunda that I know of:

1. The ambiance track composed by Jeremy Soule.

2. The Smaller moon of the two moons of Nirn which orbits Masser, the larger moon.
Person 1: Hey, have you heard Secunda?

Person 2: I Haven't.

Person 1: Have you played The Elder Scrolls V: Skyrim?

Person 2: Yeah.

Person 1: It's one of the ambience tracks in The Elder Scrolls V: Skyrim.
by Origorath, The Mad God November 22, 2020