To splurge is to indulge yourself. You can also go on a splurge if you spend a lot or act extravagantly in another way.
Anyone might have a cupcake. If you have 10 cupcakes, that's a splurge. When you go on a splurge or are splurging, it usually applies to money. Splurging happens when you see a lot of things you want — or even one very expensive thing — and buy it, even though you might not be able to afford it. When you splurge, you're going wild in some way. A splurge is sometimes called a binge.