To spill liquid messily over the edge of a container or to walk messily through mud or water.
Slopped can make people think of making a mess or being careless.
Examples:
She slopped water on the floor.
The milk slopped over the edge of the glass.
He slopped through the mud on his way to school.
The dog slopped through the puddle and got all wet.
She slopped so much soup that it went everywhere!
The paint slopped all over the table and made a big mess.