Terms are called like terms if they have the same set of variable bases and corresponding exponents.

When like terms are added or subtracted, they can be combined.

When unlike terms are added or subtracted, they cannot be combined.

When 2 apples and 4 apples are placed together (added together), the result is 6 apples.

Similarly in algebra, 2x and 4x are like terms. When they are added, they can be combined to give 6x.

When 2 apples and 4 cups are placed together (added together), the result is 2 apples and 4 cups. They cannot be "combined"

Similarly in algebra, 2x and 4y are NOT like terms. When they are added, the result is 2x + 4y.

When unlike terms are added, they cannot be "combined".

5x² and -2x² are like terms. The sum of 5x² and -2x² is 3x².

2x and 3 are NOT like terms. The sum of 2x and 3 is 2x + 3.

3x²yz³ and 8x²yz³ are like terms. The sum of 3x²yz³ and 8x²yz³ is 11²yz³.

4x²y and 4xy² are NOT like terms. The sum of 4x²y and 4xy² is 4x²y + 4xy².

5x²y and 2yx² are like terms. The sum of 5x²y and 2yx² is either 7x²y or 7yx².

5x³y² and 5x²y³ are NOT like terms. The sum of 5x³y² and 5x²y³ is 5x³y² + 5x²y³.