Untyped Plutus Core
One key feature of Aiken is how it helps you manipulate Untyped Plutus Core (abbrev. UPLC in short). UPLC is ultimately the format whereby codes gets executed on-chain. This is pretty-much as low-level as you can get when it comes to Cardano smart contracts. Note however that on-chain, UPLC code is encoded in a binary encoding for conciseness.
Understanding how UPLC works, and having the right tools to troubleshoot UPLC programs can be handy when developing contracts on Cardano. Fortunately, this is something Aiken can help you with.
While UPLC has erased any explicit notion of types; functions, variables and constants are still implicitly typed and, an interpreter will raise errors when encountering a type mismatch.
For the sake of simplicity, we might speak about the type-signature of
builtin functions such as addInteger which, in principle, only has a
concrete meaning in Typed Plutus Core. Hence, even though they are untyped,
we often think of UPLC programs has having implicit types, as if they were
originally typed programs whose types had simply been erased (in fact,
that's exactly what they are).