Wikipedia
Rekhta (, rextā) was the Hindustani language as its dialectal basis shifted to the Khariboli dialect of Delhi. It's considered one of the Urdu dialects. Rekhta means "scattered" but also "mixed" and implies that it contained Persian and Hindvi/Hindi. The term Rekhta was in greatest use from the late 17th century until the late 18th century, when it was largely supplanted by Hindi/Hindwi (Hindavi) and later by Hindustani and Urdu, though it continued to be used sporadically until the late 19th century. Rekhta-style poetry is still produced today by Urdu speakers, and is the most common linguistic form of writing poetry in the Urdu language. Rekhta is a very versatile language, and can grammatically change to adapt to Persian grammar, without sounding odd to the reader.
The following popular sher by Mirza Ghalib also tells us that the linguistic term rekhta was extended in 19th century North India to poetry written in the 'rekhta' vernacular (as opposed to poetry written in Persian, then considered the classical language)
Rexte ke tum hī ustād nahīṅ ho ğālib , ''Ghalib, you are not a master of Rekhta" , Ghalib, you are not the sole grand-master of rekhta [Translated from Urdu]
Kihte haiṅ agle zamāne meṅ koī mīr bhī thā, They say, in ages past, that there was one called Mir .
Correct stanza is Kehte hain ke aglon me koi meer bhi tha - it is said that (in) formers there was someone (named) meer [Urdu Translation]
Rekhta was also used for forms of poetry like Masnavi, Marsia, Qaseedah, Thumri, Jikri (Zikri), Geet, Chaupai and Kabit.