It would probably be most accurate to say that it's an extra person.

Verbs can be inflected in various languages for gender, number, person [which can include degrees of formality, respect, or social distance], voice, mood, tense, aspect, ergativity [an alternative to voice], evidentiality [how the speaker knows that the thing happened], and other things I'm probably forgetting.

Yes, I know. As far as I know, Mexican Spanish has all the same tenses as European Spanish but lacks a second person familiar plural, and hence the associated form of the verb in each tense.

The first person informal plural (vos, vosotros) form of verbs isn't used outside Spain. Or maybe it's just not used in Latin America. Source: high school Spanish.

There are parts of south america where vosotros is used, but I think what the parent was getting at is that it is not technically considered a 'tense', but rather a 'person' as in e.g. 'third person'

In Colombia, the use of 'vos' means the person is from the region where sugarcane is cultivated, or the cities around.

That means Cali, Buenaventura and some others.

Yes, that's why I said "because of vosotros" in my post.

I thought it was used in Argentina at least?