An indicative price is a reference number: it says roughly where a market is, but nobody has committed to trade at it. An executable price is a commitment — a quote a counterparty will actually deal on, for a stated size, for as long as it stands. Chart feeds, news tickers, aggregated rate pages and many mobile widgets carry indicative prices; the numbers on your dealing ticket are meant to be executable.
Confusing the two produces avoidable complaints. A rate seen on a third-party site is not evidence that a broker mispriced you, because that site was not offering to trade with anyone. Executable prices are also size-dependent: a quote good for a small ticket is not automatically good for a large one, and in thin conditions a streamed executable price can be withdrawn before an order reaches it. Establishing which kind of price you were looking at is the first step in any dispute about a fill.
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Guide
How Execution Models Work: ECN, STP and Market Maker
Market maker, STP and ECN describe where the other side of a trade comes from — and what each model changes about spreads, requotes and order handling.