Short answers, pulled from the story.
A military salient, also called a bulge, is a battlefield feature that projects into enemy territory and is surrounded by the enemy on multiple sides. This makes the troops occupying it vulnerable, since a deep salient can be pinched off through its base.
A salient becomes a pocket when it is pinched off at its base, cutting the encircled forces from their supply line. A pocket also implies the trapped forces did not choose to be surrounded, unlike a fortified position under a deliberate siege.
The Mule Shoe Salient was a bulge in the Confederate Army of Northern Virginia's trench line at the Battle of Spotsylvania, formed where the line curved forward to protect a piece of high ground. Union troops broke through it, and 22 hours of brutal, hand-to-hand fighting followed before the Confederates pulled back to a new position.
British forces occupied a large salient at Ypres for most of the First World War, and the sector became one of the bloodiest along the Western Front. When British infantry said 'The Salient,' it was understood they meant Ypres.
The Soviet Union held a massive salient at Kursk that was 150 kilometers deep, making it a target for a Nazi German pincer attack. It became the site of the largest tank battle in history and a decisive battle on the Eastern Front.
The Battle of Boyra was fought by the Indian Army and the Mukti Bahini against the Pakistan Army over the Boyra salient during the Bangladesh Liberation War. Control of that salient meant control of the ground overlooking the Jessore Road, an important supply route.