The CBSE typically used to give the 3 different paper sets for their exams to Delhi, All India (also known as Outside Delhi), and Foreign.
The “C” probably refers to Compartment and (c) meaning copyrighted material of CBSE.
In 2018 they gave a single paper with disastrous results when all the papers were leaked out and distributed over Whatsapp and Facebook within minutes well before exams started.