Bråttom means 'in a hurry' or 'rushing', but there are a few things you need to know in order to use it correctly.
If you're talking about a person who's in a hurry, you would use the verb ha (to have), as in: jag har bråttom just nu (I'm in a hurry at the moment), but if you're describing a hurried situation more generally, you use the construction det är bråttom (it's a rush).
A common way of using bråttom is with the preposition med (with), for example nu är det bråttom med en lösning (now we need a solution fast) or jag har bråttom med körkortet (I need to get a driving licence in a hurry).
This penguin is very important and has bråttom. via GIPHY
For extra colloquial Swedish points, try the more informal term brådis – as we've mentioned before, cutting off the end of a word and replacing it with the suffix -is is typical of Swedish slang.
Centuries ago, the word *brēþaz meant 'in a hurry' as well as 'hot'; it comes from an even older word meaning 'steam/vapour'. But over the centuries, the connotation of heat got lost so that in Old Norse bráðr meant 'sudden', which developed into bråd ('sudden' or 'fast') in today's Swedish.
You don't hear bråd all that often in Swedish, and if you do, it's usually in phrases such as en bråd tid (a busy time) or en bråd april (a busy April), or the set phrase en ond bråd död ('an evil, sudden death', used to refer to a murder). There's also the compound adjective brådmogen, which literally means 'rush-mature' and refers to someone who is grown-up for their age.
From bråd comes the noun brådska, which literally means 'a hurry'. You can use it in sentences like det är ingen brådska (there's no rush/hurry), which means the same thing as det är inte bråttom (it's not a hurry). A common mistake made by English speakers is to say something like jag är i en brådska, an attempt at literally translating 'I'm in a hurry' which doesn't work in Swedish.
Instead, you just need to say: jag har bråttom.
Varför har du så bråttom?
Why are you in such a rush?
Jag har lite bråttom just nu så jag kommer inte att hinna svara på alla meddelanden
I'm in a bit of a rush at the moment so I won't have time to answer all the messages