Sinking Fund
Money saved monthly toward a known irregular expense, so it arrives as a plan rather than a shock.
A sinking fund is money set aside on a schedule for an expense you know is coming but that doesn't happen every month: property tax, insurance premiums, vehicle registration, holiday spending, a roof or a car replacement. You pick the target amount and the date it's needed, divide by the months in between, and treat that figure as a regular bill.
The point is that these costs are predictable in aggregate even though they're lumpy in timing. A budget that only counts monthly expenses will look healthy eleven months a year and then get wrecked by an annual premium, which is usually the moment a credit card balance appears or an investment gets sold at a bad time. Naming each fund separately also stops one pot of savings from quietly covering three different obligations.
A sinking fund is not an emergency fund, and treating them as one account defeats both. An emergency fund exists for the things you cannot foresee, and it should stay intact. A sinking fund is for the things you can foresee, and it is meant to be spent, on schedule, without that counting as a setback.
This definition is general information to help you understand a term, not financial, tax, or legal advice. Figures that change year to year (limits, thresholds, rates) should be confirmed against current official sources. For guidance on your situation, a licensed fee-only fiduciary is the right next step.