What's the difference between legal and physical custody?
Legal custody is who makes the decisions. Physical custody is where the children live. They are separate, they are decided separately, and it is common to have a different arrangement for each.
Almost every confusing custody conversation comes from these two being treated as one thing.
Legal custody: who decides
The authority to make significant decisions about a child's upbringing. In practice that usually means schooling, non-emergency medical care, and religious upbringing, with day-to-day choices left to whichever parent has the children at the time.
Joint legal custody means both parents share that authority and are expected to consult each other. It is the common arrangement, including in many cases where the children live mostly with one parent.
Sole legal custody means one parent decides. Courts order it less often, generally where the parents cannot communicate at all or where there are safety concerns.
The word "joint" hides the question that actually causes trouble: what happens when you disagree. A plan that says "joint legal custody" and stops has not answered it. Better plans assign categories to each parent, or name a tie-breaker, or require a specific process before either parent acts alone.
Physical custody: where they live
Where the children actually are, night by night. This is what most people mean when they say custody.
It gets described as primary, shared, or joint physical custody, and those labels mean different things in different states, which is why the schedule matters more than the label. A plan that says "joint physical custody" without a calendar has not settled anything. A plan with an actual week-by-week schedule has, whatever it is called.
Why the distinction matters
They combine independently. Children living primarily with one parent while both share decision-making is an extremely common arrangement.
Support usually tracks physical custody, not legal. Who decides about school does not usually change who pays what.
Access to records is broader than legal custody. For school records at any school that takes federal education funding, federal law gives both parents access, custodial and non-custodial alike, unless the school has been given a court order, a state statute, or another legally binding document that specifically revokes it. Most private and religious K-12 schools take no federal funding and sit outside that rule, so there the answer depends on the school and on your order. That access also belongs to you only while your child is a minor in school: the moment they turn 18 or start college, whichever comes first, the records become theirs, and you need their written permission to see anything, even if you are the one paying tuition under the decree. Medical records depend more on your order and your state, though joint legal custody commonly carries the right to obtain them, and a provider can decline to hand them to a parent when it believes doing so could put the child at risk. Either way you can usually ask the school or the doctor directly rather than going through the other parent, and many parents spend years asking their ex for information they could have requested themselves.
The words people actually use
Custodial and non-custodial usually refer to physical custody, and people use them fluently even when the labels do not match their actual order.
Many states have moved away from "custody" altogether toward parenting time and decision-making responsibility, partly because the older words make it sound like a prize. Your paperwork may use either vocabulary.
What to focus on instead of the labels
The label matters far less than the specifics. Who has the children which nights, how holidays work, who decides what and what happens when you disagree, how far one of you can move, and what happens when the plan needs to change.
What goes in a parenting plan covers the full list, including the point most worth knowing early: the temporary arrangement you agree at the start has a way of becoming the permanent one.
What each label means, and what a court will presume in the absence of agreement, vary substantially by state. Have any parenting arrangement reviewed by a licensed family-law attorney where you live before it becomes an order.