Trade sale = someone bigger than you buys your company outright. For the buyer, your company/it’s business are a nice complementary add-on to what they already have (they have a brand, customers, channels, salespeople etc – but they have a critical hole your company could fill)
Early Stage = this refers to the stage your business is at, not to the calendar age of the company. The sweet spot is that you have found (at least v1.0) of your product/market fit and demonstrated sufficient proof of it working in real life, but you have not yet built “real” business of it.
In essence, in an early stage trade sale the seller sells a recipe for growth for a buyer who believes they can do the baking of that growth based on that recipe.