Rädd means 'scared', 'frightened' or 'afraid', and is used as an adjective. If you're talking about more than one person, you use the plural for, rädda, for example vi var rädda (we were afraid), but pay attention to context, because rädda is also a verb meaning 'to rescue'.
Hear how rädd is pronounced in the clip below:
Although 'scared' is the usual meaning of rädd, different prepositions can change the meaning quite a lot.
You'll probably most often see rädd followed by the preposition för and a noun, or för att and a verb, and this translates as 'scared of'. For example: Jag är rädd för fåglar (I'm scared of birds), jag är rädd för att bli kär (I'm scared of falling in love).
And rädd can also come before the noun, for example en rädd pojke (a frightened boy), en rädd kanin (a frightened rabbit).
There are several words in the same lexical family as rädd: en rädsla is the noun form, meaning 'a fear', so you might say jag har en rädsla för att flyga (I have a fear of flying). Then there are a few compound words which work as adjectives. Most of these describe common fears, so jag är mörkrädd means 'I'm scared of the dark', and vi var livrädda means 'we were scared for our lives', although the latter is often used for emphasis rather than being reserved for life-or-death situations.
Rädd can also be used to talk about a negative suspicion, in which case it's usually followed by att, for example, jag är rädd att det är så (I'm afraid that it might be the case). In this case, the person isn't necessarily describing something they experience as frightening, but just something generally negative which they think is the case. In English, you could translate the example sentence as 'I'm afraid this might be the case' or even 'I fear that might be the case', but you wouldn't translate rädd as 'frightened' or 'scared'.
And you can also follow rädd with the preposition om. In this case, vara rädd om generally means something like 'I'm worried about' or 'I'm careful about'. For example, you might see signs warning you Var rädd om vår miljö or Var rädd om er. These are best translated as 'Think about the environment/take care of the environment' or 'Look out for yourself/Be careful'.
This can be very confusing for non-native Swedes: if someone tells you var rädd om dig (take care of yourself) they might interpret it as 'be afraid of yourself' and wonder what the speaker knows that they don't. It also shows the importance of prepositions, since if you say min mor är rädd om mig (my mother takes care of me) and min mor är rädd för mig (my mother is afraid of me), those are two very different sentences.
Rädd comes from an old Swedish verb, räda, which literally meant 'to frighten' but is no longer used in standard Swedish. Today, you would use the verb skrämma to say 'to frighten/scare'.
Jag är inte rädd för någon
I'm not scared of anyone
Jag blev rädd när jag såg spöken
I was scared when I saw the ghost