Learn Hardcore Russian: Это факт.

Это here is a demonstrative pronoun (often called a “dummy subject”) that introduces or identifies something. In English it corresponds to “this is,” “that is,” or simply “it is.” Russian does not use a linking verb in the present tense, so Это + noun is how you say “This is a [noun].”

Why isn’t there any verb like “to be” in Это факт?

In modern Russian the verb быть (“to be”) is normally omitted in the present tense. You would use a form of быть in the past or future (e.g. Это было фактом, Это будет фактом), but for present statements you simply say Это + noun (or adjective).

Why is факт in the nominative case?

After Это the noun remains in the nominative because it is a predicate nominative (a noun complement linked to the subject). In other words, Это and факт form a simple “X is Y” construction without an explicit verb, so both parts stay nominative.

What’s the difference between Это and Этот?