Suspense. A state of mental uncertainty, to use the dictionary answer. In writing, suspense is making the end of the book uncertain.
Short term suspense is making the end of a scene uncertain. Here's an example from my own writing;
Aron crouched, just outside the Satpaba camp. He shrugged his shoulders, feeling the unaccustomed weight of Satpaba armor on his shoulders, taken from a fallen enemy.
A low whistle rang out; Aless's all-is-ready signal.
Before Aron was a small pile of branches and kindling, and in his hands was a flint. In order for the plan to work, Aron had to light a fire.
"This better work." Aron muttered.
He gritted his teeth, and then struck the flint. It showered sparks on the kindling, but it didn't catch fire. It surprised Aron; he hadn't taken into account that the fire might not light. Come on, this wood must be the dryest in Aleorendos!
Whether it was just the dawn air or some spell of the evil place, the kindling wouldn't light. Aron struck the flint again, harder this time. One of the men nearby jerked up his head, hearing the sound.
"Come on..." Aron urged the kindling, blowing on it softly.
The man walked slowly toward Aron's hiding place, listening.
One of the sparks burned slowly, without flame. Aron blew on it, causing it to grow slightly.
The man walked closer...
The small spark winked out. "No!" Aron hissed. "Come on, Saar, help me! Light!"
Whoosh! The entire pile of kindling suddenly burst into hot flames. Aron scrambled backward to avoid the fire, and the man leaped backward with a curse, shouting to his comrades.
See what I mean, now? The kindling in the scene wouldn't light, and a man from the enemy camp was approaching. This is called (at least by me) short term suspense.
I was trying to make the reader think that the fire might not light. If I can successfully do that, I can probably pull it off with long term suspense.