What Is the Difference Between Mincha Gedolah and Mincha Ketanah?

Shalom u'vrachah 

From half an hour after midday until sunset, the time for the Mincha prayer continues. However, ideally one should wait for the time of Mincha Ketanah, the point marking the halfway point between the beginning of the Mincha time and the end of its time. Mincha Gedolah, by contrast, is the name for the beginning of the time, from half an hour after midday until the time of Mincha Ketanah; then Mincha is prayed by those who estimate that they will not be able to pray Mincha after the time of Mincha Ketanah. The time of Mincha Ketanah is the time when the daily afternoon offering was brought in the Temple, and only on rare occasions was the daily offering brought at the time of Mincha Gedolah. Today, the time of Mincha Gedolah began at 11:53 in Jerusalem and continues until 2:37. At 2:37, the time of Mincha Ketanah began, and it continued until 4:54 at sunset. 

B'hatzlachah - Menashe Yisrael