How are negative keywords different from other keywords?
They can increase your costs.
They prevent your ad from showing for search terms that you don’t want.
They make your ad appear for search terms that you don’t want.
They can only be used for ads on the Display Network.
For search campaigns, you can use broad, exact, or phrase match negative keywords. However, these negative match types work differently than their positive counterparts. The main difference is that you’ll need to add synonyms, singular or plural versions, misspellings, and other close variations if you want to exclude them.
For Display and Video campaigns, negative keywords are always considered exact match. You won’t be able to change the match type for negative keywords you add to Display and Video campaigns.
Read more here: https://support.google.com/adwords/answer/2453972