Snömos defines two different kinds of snow, which are equally common in Sweden.
Mos means 'pulp' or 'mash' (you might recognize it from potatismos, meaning 'mashed potatoes') and snömos is the kind of greyish slushy substance that covers the streets a few days after heavy snowfall, where the initial snow has begun to melt and mix together with grit, mud, and dirt from people's shoes and cars.
There are several other names for what in English is called 'slush'. You can also call it snösörja (literally 'snow sludge', which is a beautiful word since sörja as a verb means 'to mourn', giving it a sense of sadness), slask (sludge), or modd (melted snow which is usually mixed with mud).
But confusingly, snömos can also refer to fresh, fluffy snow. There's a creamy dessert made of egg whites, cream, spices and fruit that is known as snömos too, and if you follow the recipe correctly it should look like fresh snow rather than days-old gritty slush. Sometimes, whipped cream itself is referred to as snömos, especially among Swedish-speaking Finns.
Snömos can also be used in a metaphorical sense.
If you say that someone is serving or producing snömos, it means they are talking with beautiful imagery or powerful ideas, but no substance. It's often used about politicians who offer plenty of rhetoric but less concrete options, or you might use it about a boss who talks about company values that are rarely acted upon, an article that fails to get to the point, or anyone else who uses meaningless phrases or empty promises. The idea behind this image is that the words are similar to fluffy fallen snow: they will soon melt to nothing.
Hon lovade mycket, men det var bara en massa snömos
She promised a lot, but it was just a load of empty talk
Snön har blivit till snömos
The snow has become slush