Summary [TLTR]: Admin, when talking about Functional Expense allocations may not coincide with the Term “overhead” use by a funding source. You need to find out what the grant application or funder means by Overhead.
First and foremost, in the nonprofit world, is the functional allocation percentages. You see these functional expense breakouts on your IRS Form 990 and your financial statements. Program Expense, Management & General (aka Admin) and Fundraising. There is a slew of guidance on breaking these out in GAAP (Generally Accepted Accounting Principles) and by the IRS (form 990 instructions-revenue rulings etc.) This is the Percentage the “Charity Rating Agencies” use. Funders and grantors use these agencies to help determine the contributions or grants they are making. You have heard of GuideStar, Charity Navigator, Charity Watch etc. As with all allocations there are a lot of assumptions and flexibility (i.e. how much of Salary, Rent, other expense should be in Program vs. Admin). In smaller nonprofits, much is allocated because everyone does everything. You know what I mean…
When dealing with some grants (especially government grants) or in some other places, they may ask about overhead percentage (or even use the would Admin, but in a different light). This really could vary from thing to thing. But this Overhead percentage and the Function Expense allocation (see above) may not coincide. For example, part of your occupancy (rent) will definitely be in Program Expenses. But a specific grant or government funder may consider occupancy 100% overhead. Overhead, in some circumstances, really pulls out anything that is not a very direct cost. But you have to look at the specifics of whoever is asking. There could still be allocations. But different. Maybe a grant allows the salary of a specific person (executive director) to be max 10% allocated to program (and the rest be Overhead).
Since Overhead is not a standard term, you must look at the definition that the specific grant is using. A good tool to figure out what a specific funder means by overhead is to find the report you will send them (they will probably require a quarterly or annual report of some sort). That is what they will look at to see if you are meeting the requirements. Find that and the instructions. That will explain what overhead is in that case.