This is the 8277th most frequent Russian word.
машу
The Russian word "машу" means "I wave" (first person singular of "махать" – to wave).
Here 'машу' means 'I wave', showing an action of waving a hand in greeting.
Я машу рукой и кричу: «Привет!»
I wave my hand and shout: "Hello!"
In this case, 'Машу' refers to a person's name, specifically the object form of 'Маша', used as a direct object in the sentence.
Машу часто видят гуляющей в парке.
Masha is often seen walking in the park.
Here, 'машу' again is the object form of 'Маша', indicating that Masha is being used as a medium for sending regards.