vyāṁ vyāsadevāya namaḥ
Dear Anand, Namaste.
Varga-uttama = vargottama.
Uttamāmśa arises when a planet is strong in 3 vargas. In case of same sign in D1 and D9 you will also find the planet occupying the same sign in Jagannātha Drekkana (J3) ALWAYS. Hence the term vargottama specifically applies to the D1 & D9 and thus implying the J3 as well.
Many stretch the term to other vargas viz-a-viz the D1 which technically we should term varga-pārijāta (strong in 2 vargas is Pārijātāṁśa). However, the meaning of vargottama w.r.t. the D9 differs in the results compared to that of other vargas viz-a-viz the D1.