From the perspective of 1787, it would be like requiring a definition of the word "foot."
Anyone who would need one is probably too stupid to understand one. I would suggest you could figure out the meaning by looking how it worked in practice.
100,000 Children born to British Fathers in the United States after July 4,1776 and before September 3, 1783 (Treaty of Paris) were recognized by both the US Government *AND* the British government as NOT American citizens.
Several Millions of blacks born in the United States after July 4, 1776, and before July 9, 1868, *NOT* recognized by the US Government as American Citizens.
Several Million Indians born in the United States after July 4, 1776, and before June 2, 1924, *NOT* recognized by the US Government as American Citizens.
Are you getting the gist of how it worked in practice? Do you know how many violations of that "born on the soil" theory there were? Millions. So many that it demonstrates the theory to be patently absurd.