The yellow squared are "adjacent" to the red square.
From: https://www.merriam-webster.com/dictionary/adjacent Definition of adjacent1a:
not distant : NEARBY the city and adjacent suburbsb: having a common endpoint or border adjacent lots adjacent sides of a trianglec: immediately preceding or following In this case "b" is the relevant definition, "having a common endpoint or border".
ell.stackexchange.com/users/94904/jwh20
In this particular case, I would probably say, "The classmate who's bullying Mark must be sitting in one of the four adjacent seats."
Saying "the four adjacent seats" makes the sentence unambiguous, and it avoids using the word "orthogonally", which is a technical term that I wouldn't expect every native speaker to know.
ell.stackexchange.com/users/2020/Tanner Swett
They are orthogonally adjacent to the red square.
The green squares at the corners of the red square are diagonally adjacent .
https://english.stackexchange.com/questions/164704/is-there-one-word-for-both-horizontal-or-vertical-but-not-diagonal-adjacency/164759
If you want to be very general and elicit a subsequent barrage of clarifying questions from your intended audience about the inclusion of the diagonally adjacent squares, you could say they border or are adjacent to the red square.
ell.stackexchange.com/users/36224/EllieK
You could use a number of words including: adjacent
surrounding Adjacent would be my preference - note that the word has a more specific meaning in mathematics, but in English grammar can mean "next to" in any direction , including to the sides, in front or behind.
On its own, "next to" does tend to mean to the left or right sides.
Your suggestion of "encircling" doesn't sound quite right as the pattern of the chairs in your image is not a circle, which is is what it specifically means - to form a circle around.
"Surrounding" is synonymous with "encircling", but does not specifically mean the shape of a circle.
ell.stackexchange.com/users/66325/Astralbee
"One seat away from Mark" also identifies the seats on each side, and in front and back.
It does not exclude the diagonally adjacent seats.
ell.stackexchange.com/users/28413/user8356
Nobody has come out and said it yet, so I will.
There's nothing whatsoever wrong with "next".
The classmate who's bullying Mark must be sitting next to him.
This is perfectly normal, acceptable, every-day English that will be perfectly understood and will not seem awkward or weird at all.
It applies perfectly well to the seats ahead and behind as much as it does to the ones to the sides.
Without the drawing, a speaker may also consider the four corner desks also to be "next" to the central one, but this is not really important.
I think the rest of the answers here are making this much more complicated than it needs to be.
ell.stackexchange.com/users/8589/J...
Immediate You could say that those positions are immediately surrounding the central point If we look at the definitions for " Immediate ", we can see: Having no object or space intervening; nearest or next and Having a direct bearing
This becomes more clear if we remove the space from between the objects in the image.
The green objects are obstructing the yellow objects.
In other words, there is no direct, unobstructed path from the red square to any of the yellow ones.
ell.stackexchange.com/users/117619/AlgoRythm
Another term would be " contiguous ": Definition of contiguous 1: being in actual contact : touching along a boundary or at a point "the 48 contiguous states"
ell.stackexchange.com/users/81057/Codex24
Let's say you are in a classroom. You are the red square. What to call the position of the yellow seats in relation to you?  I thought of using "next," but I think that doesn't apply to the seats in front and behind the red square.  I also thought of "encircling," but that would include the green squares on the corners.  Example sentence:   The classmate who's bullying Mark must be sitting __
What do you call this nearby position?
ell.stackexchange.com
<word-request><phrase-request>
ell.stackexchange.com/questions/252451
ell.stackexchange.com/users/1806/alexchenco
 You could use a number of words including:   adjacent, surrounding   Adjacent  would be my preference - note that the word has a more specific meaning in mathematics, but in English grammar can mean "next to" in  any direction , including to the sides, in front or behind. The following are all suitable options: "contiguous", "next to", "immediately surrounding", "adjacent", "orthogonally adjacent", "diagonally adjacent", "border" — "encircle" is a less likely option. 
The following are all suitable options: "contiguous", "next to", "immediately surrounding", "adjacent", "orthogonally adjacent", "diagonally adjacent", "border" — "encircle" is a less likely option. 