Step 1: Identify the pattern in the sequence.
List the letters with their positions in the alphabet:
\[
A(1), Z(26), G(7), T(20), M(13), N(14), S(19), \_, Y(25), B(2)
\]
Step 2: Look for a pattern in the sequence.
Observing the pattern: the letters alternate between the start and the end of the alphabet, possibly mixing forward and backward moves.
Check the difference between the letters:
\( A \rightarrow Z \): from 1 to 26 (end of alphabet)
\( Z \rightarrow G \): 26 to 7
\( G \rightarrow T \): 7 to 20
\( T \rightarrow M \): 20 to 13
\( M \rightarrow N \): 13 to 14
\( N \rightarrow S \): 14 to 19
\( S \rightarrow ? \): 19 to ?
\( ? \rightarrow Y \): ? to 25
\( Y \rightarrow B \): 25 to 2
Step 3: Hypothesis:
The missing letter should be \( H \) (position 8), which fits the alternating pattern of letters moving forward and backward.
Thus, the missing term is:
\[
\boxed{H}
\]