Genseren er nuppete.

In Norwegian, the definite article is usually attached to the end of the noun.

• genser = sweater
• genseren = the sweater

So the -en at the end is doing the job of English the.

Because genser is a masculine noun in Bokmål, its usual definite singular ending is -en:

• en genser = a sweater
• genseren = the sweater

Yes. Genseren refers to a specific sweater, usually one that is already known from the situation or the conversation.

For example:

• if you are looking at a sweater and commenting on it, Genseren er nuppete sounds natural
• if you are introducing it for the first time, you would more likely say something like Jeg har en genser. Den er nuppete.

So the definite form often implies the sweater we are talking about / the sweater here.

Er is the present tense of å være (to be).

Unlike English, Norwegian does not change this present-tense form depending on the subject:

• jeg er = I am
• du er = you are
• han er = he is
• vi er = we are

So in Genseren er nuppete, er simply means is.

Nuppete is the normal form of this adjective. It is one of those adjectives that already end in -e as part of the word itself.

So you get:

• en nuppete genser
• genseren er nuppete

In other words, the -e here is not something added just for this sentence; it belongs to the adjective.

Yes. This sentence has the same basic order as English:

• Genseren = subject
• er = verb
• nuppete = adjective/complement

So it follows:

subject + verb + adjective

That gives:

• Genseren er nuppete.
• The sweater is pilled/bobbly.

A useful extra point: Norwegian often follows the verb-second rule, so if you move something else to the front, the verb still stays in second position:

• I dag er genseren nuppete. = Today the sweater is pilled.

Yes, but it means something a bit different.

• Genseren er nuppete = The sweater is pilled
• Den genseren er nuppete = That sweater is pilled

So den genseren is more specific and often sounds contrastive, as if you are pointing at one sweater rather than another.

If you just mean the sweater, genseren is enough.

A rough learner-friendly guide:

• genseren ≈ YEN-seh-ren
• nuppete ≈ NUH-peh-teh

A couple of useful notes:

• the g in genser is pronounced like y in many standard pronunciations
• the r sound varies by dialect
• the vowels are shorter and cleaner than many English speakers expect

The exact pronunciation depends somewhat on dialect, but those approximations are a good starting point.

No. It can be used for other fabrics and clothes too.

For example, you could use it about:

• sweaters
• socks
• blankets
• coats
• other textiles

It describes fabric that has developed little pills or fuzz-balls on the surface. So it is common with clothing, but not limited to sweaters.