Pantheism I've heard of, but not panentheism. As the sources below indicate, the two pan -isms are closely related, but different. So, we'll start with the one I'm unfamiliar with before getting to the one I know.
“Panentheism” is a constructed word composed of the English equivalents of the Greek terms “pan”, meaning all, “en”, meaning in, and “theism”, meaning God. Panentheism understands God and the world to be inter-related with the world being in God and God being in the world. It offers an increasingly popular alternative to traditional theism and pantheism. Panentheism seeks to avoid both isolating God from the world as traditional theism often does and identifying God with the world as pantheism does. Traditional theistic systems emphasize the difference between God and the world while panentheism stresses God's active presence in the world. Pantheism emphasizes God's presence in the world but panentheism maintains the identity and significance of the non-divine. Anticipations of panentheistic understandings of God have occurred in both philosophical and theological writings throughout history (Hartshorne and Reese 1953; Cooper, 2006). However, a rich diversity of panentheistic understandings has developed in the past two centuries primarily in Christian traditions responding to scientific thought (Clayton and Peacocke 2004).Of the two, my thinking is more in line with pantheism. What's your opinion re the two pans?
~ Stanford Encyclopedia of Philosophy ~
Panentheism (from Greek πᾶν (pân) "all"; ἐν (en) "in"; and θεός (theós) "God"; "all-in-God") is a belief system which posits that God exists and interpenetrates every part of nature, and timelessly extends beyond as well. Panentheism is distinguished from pantheism, which holds that God is synonymous with the material universe.
Briefly put, in pantheism, "God is in the whole"; in panentheism, "The whole is in God." This means that the Universe in the first formulation is practically the Whole itself, but in the second the universe and God are not ontologically equivalent. In panentheism, God is not exactly viewed as the creator or demiurge, but the eternal animating force behind the universe, with the universe as nothing more than the manifest part of God. The cosmos exists within God, who in turn "pervades" or is "in" the cosmos. While pantheism asserts that God and the universe are coextensive, panentheism claims that God is greater than the universe and that the universe is contained within God.
~ Wikipedia ~
Pantheism is a metaphysical and religious position. Broadly defined it is the view that (1) "God is everything and everything is God … the world is either identical with God or in some way a self-expression of his nature" (Owen 1971: 74). Similarly, it is the view that (2) everything that exists constitutes a "unity" and this all-inclusive unity is in some sense divine (MacIntyre 1967: 34). A slightly more specific definition is given by Owen (1971: 65) who says (3) "‘Pantheism’ … signifies the belief that every existing entity is, only one Being; and that all other forms of reality are either modes (or appearances) of it or identical with it." Even with these definitions there is dispute as to just how pantheism is to be understood and who is and is not a pantheist. Aside from Spinoza, other possible pantheists include some of the Presocratics; Plato; Lao Tzu; Plotinus; Schelling; Hegel; Bruno, Eriugena and Tillich. Possible pantheists among literary figures include Emerson, Walt Whitman, D.H. Lawrence, and Robinson Jeffers. Beethoven (Crabbe 1982) and Martha Graham (Kisselgoff 1987) have also been thought to be pantheistic in some of their work — if not pantheists.
~ Stanford Encyclopedia of Philosophy ~
Pantheism (from Greek: pan = all, and theos = God) refers to the religious and philosophical view that everything in existence is of an all-encompassing immanent God, or that the universe, or nature, and God are equivalent (i.e., that "all is God"). There are two types of pantheism: "classical" and "naturalistic" pantheism. In equating the universe with God, classical pantheism does not strongly redefine or minimize either term, still believing in a personal God, while naturalistic pantheism redefines them, treating God as rather impersonal, as in the philosophy of Spinoza. In any case, what is stressed is the idea that all existence in the universe (the sum total of all that is, was, and shall be) is of the same essence as the divine. Pantheists, then, typically deny God's transcendence. The problem of evil, which is a problem for theism, is not a problem for pantheism in the same way, since pantheism rejects the theistic notion of God as omnipotent and perfectly good.
~ New World Encyclopedia ~