Ascended masters are great spiritual teachers and healers, most of whom lived as humans upon the earth. They're powerful guides who can help you understand your life's purpose, muster the courage to make significant changes, and develop your psychic and manifestation abilities.
Each ascended master has specialties such as healing, manifesting, ascension, relationships, and so forth. They come from every religion and culture, and they're nondenominational. You don't need special training or experience to gain their help.
The term Spirit Guide is the name for an entity who watches, heals, and helps you on your journey in the physical plane. The number of spirit guides varies with each person. Each Spirit Guide has a specific purpose, for example-- creative help, healing, spiritual development, connections with others, etc.
An ancestral guide is one who was related to you at one time. Whether in past lives or the previous, deceased loved ones can choose to reincarnate as guides from the other plane.