I've seen 'demasiado' used to refer to excessive quantity, meaning 'too much of something', where it seems it has to agree with the gender & quantity of the thing(s) it describes, e.g.

What type of word is demasiado?

Quantitative adverbs like demasiado (too), bastante (quite/fairly), un poco (a bit/a little), mucho (a lot/much), tan (so), tanto (so much) and muy (very) express intensity. They can modify adjectives, other adverbs or a verb.

Is demasiado an adverb?

Spanish words that can be both adjectives and adverbs, more or less. The Spanish words más (more), menos (less, fewer), mejor (better), peor (worse), mucho (much, many), poco (little, few), and demasiado (too much, too many) may be used as adjectives or adverbs.