The inner part of your cheek in your mouth is called the buccal region. There are many possible lumps that can arise from that region.
However, given that the lump is mobile, it is likely the lump is deep to the lining of the inner cheek (buccal mucosa). Possible differential diagnosis include an enlarged lymph node, tumour from the minor salivary gland or cyst.
I would suggest a visit to an ENT Specialist for an assessment.
Hope this helps and all the best!
