grammar.verbs.haber-hay
Hay: there is, there are
Hay expresses existence and never changes for plural: hay un café, hay muchos cafés. Other tenses: había, hubo, habrá — always singular.
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Explicación
Hay (from haber) introduces things whose existence is new information: hay un problema, ¿hay wifi? It pairs with indefinites and numbers, never with el/la: hay un banco, not *hay el banco.
It stays singular in every tense: había tres personas, hubo problemas, va a haber cambios. Saying *habían tres personas is extremely common but non-standard.
Hay is the impersonal present of haber; each tense has its own single invariable form — había, hubo, habrá, ha habido, va a haber — and none of them agrees with what follows. Don't confuse this existential haber with the auxiliary haber of compound tenses (he comido), which does conjugate for the subject.
Ejemplos
There are two pharmacies on this block.
Región: global
There was nobody at the office.
Región: global
There used to be one pharmacy here; now there are two and soon there'll be three.
Región: global