What is MQL5?

What it means

The language is close enough to C++ to be familiar to anyone who has written either, with built-in access to price series, indicator handles and trading functions. Programs are compiled to a binary EX5 file, which is what is distributed to users — source is not required to run one.

Why it matters

That compilation step is why buying an EA rarely means seeing its logic. You get a binary that trades your account, and its actual behaviour can only be inferred from documentation and observed trades. This is a genuine reason to prefer vendors who publish specifics about what their system does and does not do.

What this changes in practice

MQL5 is also the marketplace where most retail EAs are sold, with a rating system and a public track record on demo and live accounts. For a buyer it is one of the few places where a vendor's claims are attached to a verifiable history, which makes it worth checking even for products sold elsewhere.