Collective Numbers

Collective numbers are those that even in their singular form indicate a group of beings or things:
Eles são um quarteto famosoThey are a famous quartetCommunity Slow audio Play audio
Sometimes they indicate the exact number of things in the group, as in the example above. A quarteto is a musical group of 4 people. Other times, they are more general:
A médica salvou várias dezenas de pessoasThe doctor saved several dozens of peopleCommunity Slow audio Play audio
In this example, dezenas technically means tens, but it is used in the same way that we often use the word dozens in English. The implied meaning is that the doctor saved a lot of people, not that she specifically saved people only in groups of 12. However, if you wanted to be specific (if you were talking about a dozen eggs, for example), the Portuguese word is dúziadozenCommunity Slow audio Play audio Number, Singular, Feminine . Notice that collective numbers function as nouns.
Here are a few more common examples:

• parpairCommunity
• duoduoCommunity Slow audio Play audio Noun, Singular, Masculine
• duetoduetCommunity Slow audio Play audio Noun, Singular, Masculine
• triotrioCommunity Slow audio Play audio Noun, Singular, Masculine
• décadadecadeCommunity Slow audio Play audio Noun, Singular, Feminine
• centenashundredsCommunity Slow audio Play audio Number
• milharesthousandsCommunity Slow audio Play audio Number