Encapsulation is the overall objective of protecting components.
Low-pressure molding is a highly effective and specialized method of achieving encapsulation, particularly for sensitive electronics, due to its gentle process, fast cycle times, and strong protective qualities.
You can encapsulate something without using low-pressure molding (e.g., through potting or traditional injection molding if the component can withstand it), but when you talk about low-pressure molding, you are almost always referring to a process specifically designed for the encapsulation of delicate items.