Definition from Wiktionary, the free dictionary
Alternative forms 
Proper noun 
- (trademark) A toy made by the LEGO Company and consisting of small, coloured, plastic bricks that can be made to join together and be taken apart, used to construct buildings, vehicles, etc. (See usage notes below.)
a toy made by LEGO
LEGO (not comparable)
- Made of LEGO.
- I made a LEGO car to play with.
Usage notes 
- LEGO is a registered trademark of the LEGO Company. See the LEGO Company's page on its trademark and Wikipedia's discussion of the trademark.
- The LEGO Company states that LEGO is officially an adjective and does not advocate its use as a noun. It is given as a proper noun here because this reflects common usage of the word.
- LEGO is officially spelled in capitals, but in common usage it is often spelled with an initial capital only.