A manner of marching in file in which each person's leg moves with and behind the corresponding leg of the person ahead WordNet 3.0 & Open English WordNet

In the United States, lockstep marching or simply lockstep is marching in a very close single file in such a way that the leg of each person in the file moves in the same way and at the same time as the corresponding leg of the person immediately in front of him, so that their legs stay very close all the time. Wikipedia

Kind of marching that involves all marcher's legs moving in the same way at the same time. Wikipedia Disambiguation

Style of marching employing simultaneous, identical movements Wikidata

A step whereby the toe of one man is brought very close to the heel of the man in front. Wiktionary