na-adjective
popular; populist; plebeian; low-brow; widely liked
Describes something that appeals to or is characteristic of the general public, often with a nuance of being unsophisticated or mass-oriented. Can be neutral or slightly derogatory depending on context.
彼の政策は大衆的な支持を得た。
His policies gained popular support.
That show has mass appeal and anyone can enjoy it.
庶民的 also means 'popular' or 'folksy', but emphasizes a common-people, down-to-earth quality, often with a warmer, more positive nuance than 大衆的, which can imply mass-produced or low-brow.
Formed from 大衆 (taishū, 'the masses') + 的 (-teki, '-like, -ic').