Definition
I-TOI is the ILS (Instrument Landing System) identifier for a specific runway approach, shown in figure 10-11 of the Instrument Flying Handbook as an example. ILS identifiers always begin with the letter 'I' followed by a two- or three-letter code, and are transmitted in Morse code by the localizer so pilots can confirm they have tuned the correct approach.
Plain English
It's the call-sign style code that identifies one particular ILS approach. The 'I' tells you it's an ILS, and the rest of the letters identify which one. Pilots listen for it in Morse code on the localizer frequency to make sure they've tuned the right approach.
Context Anchor
Seen on instrument approach charts near the localizer frequency or approach information, including examples of timed approaches from a holding fix.
Derivation
The leading 'I' is the FAA convention marking an ILS identifier. The remaining letters are assigned to the specific approach -- in this example case, an approach used to illustrate timed approaches from a holding fix.
Why Pilots Care
Maintains required spacing between successive aircraft on the approach without radar vectors.
Intuition Check
Do not read I-TOI as a clearance or instruction. It is an identifier for a specific localizer signal.
Example Sentence 1
After tuning the localizer frequency, the pilot listened for the Morse code 'I-TOI' to confirm the correct ILS was identified before beginning the approach.
Example Sentence 2
The pilot adjusted speed in the hold to meet the assigned I-TOI at the initial fix.