Ubiquitous language for the ExchangeRateSDK context: indicative FX rates from exchangerate.dev, expressed without SDK or HTTP implementation detail.
Rate: The numeric multiplier giving how many units of the Quote Currency equal one unit of the Base Currency. Avoid: treating a multi-currency response payload as “a Rate”
Indicative Rate: A Rate suitable for display, analytics, and conversion estimates — not for settlement, regulated trading, or as a source of record. Every Rate in this context is Indicative unless explicitly stated otherwise. Avoid: settlement rate, executable rate, official fix (as if this API provided one)
Source: A freshness class for rate data (for example live, ecb_daily, fred_daily) — not a vendor or data-provider name. Avoid: vendor, provider, feed name
Currency:
An ISO-like code that identifies a currency (for example USD, EUR).
Avoid: Symbol (except when referring to the API query parameter name symbols)
Pair: An ordered relationship from a Base Currency to a Quote Currency. Avoid: Slug as the domain concept
Slug:
The wire spelling of a Pair (for example eur-usd) used on pair-oriented HTTP routes.
Avoid: using Slug as a synonym for Pair in domain talk
Base: The Currency that a Rate is expressed relative to (one unit of Base).
Quote: The Currency whose units a Rate measures per one unit of Base.
Derived: A Rate (or quote in a basket) obtained by triangulation from other quoted Pairs rather than a direct market quote. Avoid: Triangulated as a type or field name (may appear in explanations only)
MarketSession: The interbank market’s trading state for a response (open, weekend, or interbank_closed) — not merely a calendar label. Avoid: Session (alone), MarketState
ForwardFilled: A historical Rate or RatesSnapshot that reuses the most recent published fix because no fix was published for the requested date. Avoid: inventing a rate for an unpublished date
RatesSnapshot: A Base Currency together with a map of Quote Currency → Rate (and associated freshness), as returned for latest or historical multi-currency requests. Avoid: calling this payload “a Rate”
Conversion: The result of applying a Rate to an amount from one Currency into another. Avoid: Convert as a noun (Convert remains the verb / operations hub name)