"Lay" come from the Greek word laos, meaning "The People," as understood for example in the Constitution of the United States. From this concept comes most of the Church's terms on how the Church is arranged or "Ordered."

Think of a deck of 52 playing cards. The Cards are the Laos. The cards may be arranged or put in order in many ways, the usual being in four suite and then King through Ace or vice-versa.

As a deck of cards, maybe even shuffled, they are "The Deck," or in this image, the Laity.

Out of this deck, we take out all the twos, sixes, threes, and eights and "arrange" them by suites. We have "put them in order," or "ordered" them. They are not above or below the rest of the 36 cards., yet of the 52, sixteen are in "Order," and the others are not:
so it is with Holy Order and the Laity.

It might be good to also read "What's Clergy?"

And by the way, at St. Mark's, the Lay Staff is certainly not ordered! Lectors, Acolytes, Sub-deacons, Widows, and others used to be but are no longer. Monks and Nuns, Sisters and Brothers are considered "clerics" as they are under vows of obedience to the Church but neither are they ordered unless they have been ordained with the Laying on of Hands.