Allot/Allotment

Allotments in this document are pieces of land deeded by the government to a particular Native American person as part of the division of tribally held land.

Held In Trust (5.1)

We like to think of this phrase as a metaphorical term for a nice, warm hug. ("Shhh, now. Everything's ok. I'm holding you in trust.") In reality, though it's kind of dastardly in nature. When the government gave Native Americans allotment lands "in trust," it meant that person didn't actually own the property. It belonged to the U.S. government, who was kindly letting the person act as a trustee or agent while farming the land. For twenty-five years. Or longer. You know, depending on how the President feels about it.

In Severalty (1.2)

There's a reason why this phrase didn't survive into our modern lexicon: it's downright confusing. When you're talking real estate (which let's face it, is perplexing enough), owning something in severalty means one person owns the property. Separately. As in severed from everyone else. This is a key term in the Dawes Act, because the whole point was to end the tribal idea about land use, which was that it belonged to everybody.

Indian Reservation

Contrary to popular belief, an Indian Reservation isn't what you need in order to get some really good Chicken Tikka Masala on a busy Friday night. A reservation is land "reserved" for and managed by a Native American tribe, its sovereignty limited by federal and state or local law (source). The Dawes Act aimed to break up these communally held reservation lands into individual plots and give them to, well, individuals.

Law of Descent (5.4)

Descent—as in "descendants." The Law of Descent pertains to what happens to an article of property when the owner dies. Who gets it? The Law of Descent lays it all out.

Manifest Destiny

Before you go back and read the Dawes Act for the umpteenth time, scanning it for this phrase, don't bother. It's not in there. But understanding the policy of Manifest Destiny is kinda crucial to understanding why this document exists.

TL/DR: Basically, during this time many people believed that it was God's will and America's divine right to expand westward across the country to spread civilization and conquer the wilderness. This allowed a get-out-of-guilt-free takeover of much of the North American continent.

Partition in Force (5.4)

"Partition" is a legal term used to describe an act (by a court order or otherwise) to divide up a concurrent estate into separate portions. So in Section 5.4, when they say, "the laws of descent and partition in force", they are saying "the laws that are already in force will apply.

Pro Rata (1.4)

Pro rata is a fancy way of saying "in proportion." So when they use this phrase in Section 1 they mean, "When there isn't enough land to give every person on a reservation the amount we promised, they'll all get a proportional amount of less land."

Riparian Proprietor (7.1)

Sounds like the guy from The Shape of Water. Actually, "riparian proprietor" refers to a person who owns lands bordering a river, lake, or other watercourse. This section is making sure that the Secretary of the Interior has the final say in irrigation rights for the benefit of the people living on the reservation.

Surveyed Lands

Unless you're Disney's Pocahontas and you make it a habit to talk to inanimate objects, it's hard to get any answers from the trees and the mountains. "Excuse me, do you have a moment to talk about your ability to support livestock?" Surveying land is a complicated process of mapping out a specific area of land in regard to its geography, layout, available elements, arability, and other qualities.