The quality of being able to stick to things.
Stickiness can be good when you want things to stay together, like glue, but it can be bad when you don't want things to stick, like when your hands are sticky.
Examples:
The stickiness of the tape makes it hard to remove.
I don't like the stickiness of the syrup on my hands.
The stickiness of the gum makes it hard to get off my shoe.
The stickiness of the honey made it hard to open the jar.
The stickiness of the spider web was so strong, it caught a big bug.
The stickiness of the sticker kept it on the paper for a long time.