Gluconeogenesis is the generation of glucose from other substrates. Like many metabolic pathways it happens mostly in the liver, and is triggered by the action of insulin.
Many 3 and 4-carbon substrates can enter the gluconeogenesis pathway. Lactate from anaerobic exercise in skeletal muscle is easily converted to pyruvate; this happens as part of the Cori cycle.
Oxaloacetate (an intermediate in the citric acid cycle) can also be used for gluconeogenesis. Amino acids, after their amino group has been removed, feed into parts of the citric acid cycle, and can thus can generate glucose in this pathway.