This is the 618th most frequent Czech word.
místních
"Of the locals" or "local (plural, genitive/locative case)."
In this sentence, 'místních' is used as an adjective modifying 'lidí' (people), describing them as local.
Mnoho místních lidí se shromáždilo na slavnosti.
Many local people gathered at the celebration.
Here, 'místních' acts as a genitive plural form of the adjective, related to 'obyvatel' (residents), indicating possession or relation.
Tradice byly ovlivněny místních obyvatel.
The traditions were influenced by the local residents.
In this case, 'místních' is used in instrumental form and relates to an unspoken noun in the context, indicating 'local people.'