Platform migration is the move from one terminal or one broker's server to another: MT4 to MT5, MetaTrader to cTrader, or the same platform at a different firm. What does not travel is the whole story — MQL4 expert advisors and indicators will not run on MT5 without a rewrite, and chart templates rarely survive a change in symbol naming.
Trade history does not migrate either. Statements have to be exported before the old account is closed, and the new server's price history will differ enough to change any backtest run against it. Treat a migration as a re-validation rather than a copy: re-run the strategy on the new server's data, re-check symbol names and contract sizes, confirm the server time offset, and keep the old terminal installed until the first month reconciles cleanly.
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Guide
Choosing a Trading Platform: MT4, MT5, cTrader and the Broker's Own
The platform decides which orders you can place, whether your stops survive a closed laptop, and how much you would have to rewrite to leave. What actually differs between the options — and the point where the platform stops mattering and the broker takes over.