Slow
Use as an adverb for 'slowly'. This is what you use to ask someone to do something more slowly.
Means 'deliberate' or 'unhurried'. Used to describe a calm, measured pace, especially in speech.
Literally 'calm', but often used to mean 'take it easy' or 'slow down'.
Can you speak more slowly, please?
The internet is very slow today.
The line for the coffee is very slow.
Take it easy! We are not in a hurry.
Walk slowly, the floor is wet.
The distinction between 'lento' (adjective for nouns, e.g., 'carro lento') and 'despacio' (adverb for verbs, e.g., 'hablar despacio') is standard across the entire Spanish-speaking world.
Usage is standard. 'Lento' and 'despacio' are the common terms.
Standard usage. You will hear 'lento' and 'despacio' used correctly as in other regions.
While 'lento' and 'despacio' are standard, you might hear the colloquial 'pará un poco' (literally 'stop a bit') to mean 'slow down'.
Usage is identical to Latin America for these words. No significant variation.
Using 'lento' as an adverb. For example: *'Habla lento, por favor.'* — While some native speakers might say this colloquially, the grammatically correct and preferred word is the adverb 'despacio': 'Habla despacio, por favor.' Use 'lento' for nouns (el carro lento) and 'despacio' for verbs (caminar despacio).
Forgetting gender agreement with 'lento'. For example: *'La conexión es lento.'* — 'Lento' is an adjective and must match the gender of the noun it describes. Since 'conexión' is feminine, the correct form is 'lenta': 'La conexión es lenta.'
Using 'despacio' as an adjective. For example: *'Es un carro despacio.'* — 'Despacio' is an adverb that describes actions. To describe a noun like 'carro', you must use the adjective 'lento': 'Es un carro lento.'