Planen er teit.

Because -en is the definite ending on the noun.

• en plan = a plan
• planen = the plan

In Norwegian, the definite article is often attached to the end of the noun instead of being a separate word like English the.

Er means is. It is the present tense of å være, which means to be.

So:

• Planen = the plan
• er = is
• teit = silly / stupid / lame

No, this is a very basic Norwegian sentence pattern:

• Planen = subject
• er = verb
• teit = adjective describing the subject

So the structure is:

subject + verb + adjective

This works much like English The plan is silly.

Because teit is being used after the verb er, so it is a predicative adjective. In Norwegian, adjectives after to be do not take the definite form just because the noun is definite.

So you say:

• Planen er teit. = The plan is silly.

But when the adjective comes before a definite noun, it does change:

• den teite planen = the silly plan

That difference is very common in Norwegian:

• Bilen er rød. = The car is red.
• den røde bilen = the red car

Here, the subject is singular, so teit is the correct form.

With this adjective, the forms are typically:

• singular: teit
• plural: teite

So:

• Planen er teit. = The plan is silly.
• Planene er teite. = The plans are silly.

Also, if the adjective comes before a definite noun, you use teite:

• den teite planen

Teit is fairly common and usually sounds informal and colloquial. It can mean things like:

• silly
• stupid
• dumb
• lame

It is not extremely harsh, but it is definitely negative. Depending on tone, it can sound playful, annoyed, or insulting.

For example:

• about an idea: That’s silly / dumb
• about a person: it can sound more insulting

A rough learner-friendly guide would be:

• Planen ≈ PLAH-nen
• er ≈ ehr
• teit ≈ roughly like English tight, though the vowel is not exactly the same

A natural rhythm would be something like:

PLAH-nen ehr tite

with the main stress on the first syllable of planen.

Here are the most useful ones:

• en plan = a plan
• planen = the plan
• planer = plans
• planene = the plans

So if you want to build similar sentences:

• En plan er teit. = A plan is silly.
• Planen er teit. = The plan is silly.
• Planer er teite. = Plans are silly.
• Planene er teite. = The plans are silly.