LEGO
n. uncountablen. a brand of plastic building blocks that you snap together to make toys. You can build almost anything with them, from houses to spaceships.
n. a proprietary system of interlocking plastic bricks and components used for construction play. When used as a generic term, it often refers to the bricks themselves rather than the brand.
He spent the whole afternoon building a castle with LEGO.
The children left their LEGO scattered across the living room floor, making it a hazard for anyone walking barefoot.
While originally marketed as a simple children's toy, LEGO has evolved into a sophisticated medium for adult hobbyists to create intricate architectural models and functional robotic systems.
In its standard usage, the word is uncountable; pluralizing it as 'Legos' is common in American English but often avoided by the brand and in British English.
I bought three LEGOsI bought three LEGO setsThe brand name is technically an adjective or uncountable noun; it is more natural to say 'LEGO bricks' or 'LEGO sets' than to pluralize the word.