What does the English proverb the rain in spain falls mainly on the plain mean?

Meaning: Most of the rain in Spain falls on the plains. This is a tongue twister Odell Hepburn practiced in My Fair Lady, in which she played a flower girl. Nowadays, many people use this sentence to practice English pronunciation and mouth shape.

Vocabulary explanation:

rain British [re?n] American [ren]

n. Rain; (tropical area) rainy season, rainy day; raindrop-like falling things; electron flow;

vt. (rain) to fall, (to make) fall; to give in large quantities, (to make) to fall in large quantities;

[Example sentence]I hope you didn't get soaked standing out in the rain.

I hope you didn't get soaked standing out in the rain.

I hope you didn't get soaked standing out in the rain.

mainly English [?me?nli] American [?menli]

adv. Mostly; mainly; basically;

[Example]The stock-market scandal is refusing to go away, mainly because there's still no consensus over how it should be dealt with.

The stock-market scandal is refusing to go away, mainly because there's still no consensus over how it should be dealt with. It achieves consciousness.

plain British [ple?n] American [plen]

n. Plain; flat land; [textile industry] plain needle; unpretentious things;

adj. plain; plain; clear; plain-looking;

adv. clearly, plainly; easily; [used to strengthen the tone] obviously; completely;

[Example]In general, a plain carpet makes a room look bigger.

In general, a single-color carpet makes a room look bigger.