What is Soma then? Is it even a drink?

Yes,it is a drink from the now extinct Soma Plant.Achārya Chanakya's Arthashashtra mentions how Brahmins used to grow Soma at home in NW India on their lands granted by Kings themselves for it's production.

The immortality hymn suggests how important this drink was to the our ancestors.

Sushruta Samhita mentions 24 types of Soma drinks & the somayagya's importance is precisely why even Epic literature lists out the alternative in case of unavailability.

Dr David Frawley rejects the hypothesis that Ephedra of Iran & Afghanistan being the same as Soma since it is a dry plant with little or no juice.He instead believes that Soma in India were special powerful plants growing in mountain lakes and riverine regions of Himalayas.

Btw where are you reading all this from?