Geitonogamy refers to:

The correct answer is Option (3) → Transfer of pollen grains from the anther to the stigma of another flower of the same plant

Pollination is of three kinds, according to where the pollen comes from: autogamy (the same flower), geitonogamy (another flower of the same plant) and xenogamy (a flower of a different plant).

(1) Transfer of pollen grains from anther to the stigma of a different flower of different plants — Incorrect. This is xenogamy. It is the only kind that brings genetically different pollen to the stigma.

(2) Transfer of pollen grains from the anther to the stigma of the same flower of same plant — Incorrect. This is autogamy.

(3) Transfer of pollen grains from the anther to the stigma of another flower of the same plant — Correct. This is geitonogamy. It needs a pollinating agent, so it is cross-pollination in its working. But the pollen comes from the same plant, so genetically it is like autogamy.

(4) Transfer of pollen grains from the anther to the stigma of the flowers of different species of plants — Incorrect. This is not one of the three kinds of pollination.

NCERT Extract:
Pollination – “… Geitonogamy - Transfer of pollen grains from the anther to the stigma of another flower of the same plant. Although geitonogamy is functionally cross-pollination involving a pollinating agent, genetically it is similar to autogamy since the pollen grains come from the same plant.”