This is the 3042nd most frequent Polish word.
pociągi
"Trains"
Here, 'pociągiem' is used in the instrumental case to indicate means of travel, 'by train'.
Codziennie podróżuję pociągiem do pracy.
I travel by train to work every day.
In this sentence, 'pociągi' is used as the subject of the sentence in the nominative plural form, signifying 'trains'.
Pociągi w Polsce są coraz szybsze.
Trains in Poland are getting faster.
Here, 'pociągi' is used in the accusative plural form as the object of the verb 'oglądać', meaning 'trains'.