hover
verb
gerund or present participle: hovering
1. (used about a bird or HELO etc.) to stay in the air in one place
2. (used about a person) to wait near somebody/something
Infill: the use of vacant land and property within a built-up area for further construction or development
a substance or material used to fill in
Jackstall - an aeronautical condition and occurs when the blades overpower the hydraulic servos - the jacks stall - and the controls lock solid.
If you're training in a Robinson that may not mean much because it doesn't have hydraulic controls.