What is a jatisvaram ?

Jatisvaram/ jathiswaram :

After the students learn geethams, couple of swarajathi the next they learn is jatiswarams.

Jatisvaram is a composition very much like the svarajati in point of musical
structure, but has no sahitya and the piece is sung with the solfa syllables.
It is a composition belonging to the realm of dance music. It is also known
by the word ‘svara-pallavi’. Due to the number of Jatis in Svara Pallavi, it is
known as Jatisvaram.

Check out Gowli jathiswaram here.