1. Level of Organisation 

a. Protoplasmic or acellular level: The organism in which all the activities are performed  by singled celled organization.for example: protozoa or some acellular Protista.

b. Cellular level: The organisation in which organisms are made up cells.Cells do not show coordination with each other and performs all the activities independently by the general body surface. for example mesozoans and sponges.

c. Tissue grade organisation: An organisation is which organisms consists of tissues. Coelenterates are supposed to make the beginning of the tissue grade. They are diploblastic.

d. Organ grade organisation: An organisation in which animals consists of organ for specific function. Platyhelminthes are the first to reach to this level of organisation. They are triploblastic.

e. System grade organisation: An Organisation in which animals have well developed system. It was first seen in Nemerteans. Aschelminthes, annelids and all the other higher phyla show this kind of organisation.

2. Body Plan 

a. The cell aggregate plan: They have only clusters of cells with no co- ordination between cells. for examples-sponges

b. The blind sac plan: They have digestive cavity with only one opening to the outside through which ingestion as well as egestion occurs. For e.g.  coelenterates and flat worms 

c. The tube within a tube plan:  Tube within tube body plan means that the animal body consist of two tubes,one formed by the body wall and second formed within the digestive tract.It has two openings or ends ( anterior end - mouth and posterior end - anus). For e.g. Earthworm, man, frog etc. 

3. Body symmetry 

a. Asymmetry: If the body of an organism cannot be divided into two equal & similar halves by any dividing planes (lines passing through the centre) it is called asymmetrical animal.for e.g. sponge, amoeba etc.

b. Bilateral symmetry: If the body of an organism can be divided into two equal and identical halves by only one dividing plane. For e.g. some invertebrates and all vertebrates(Platyhelminthes up to chordate).

c. Radial symmetry: If the body of an organism can be divided into two equal and identical halves by many dividing planes.For e.g. simple sponges, coelenterates, adult echinodermata etc.

d. Biradial symmetry: When body can be divided into two equal and identical halves only by one or two vertical planes. For e.g. sea anemone.

4. Body cavity( coelom)
The cavity found in between the body wall and the alimentary canal wall is called coelom. It may be of following types:

a. True coelom: It is the cavity formed by the splitting of solid mesoderm during embryonic development. It is found in annelids, mollusks and chordates.

b. Pseudocoel: The coelom that arises from the first embryonic cavity blastocoels filled with muscles. For e.g. roundworms, nematode, rotifera.

c. Acoelomate: Animals which lack the coelom, are called acoelomates. examples_ Porifera, coelenterates and  Platyhelminthes.

d. Haemocoelomate: The coelom developed during early development latter filled with blood or blood likes colourless fluid. e.g. Arthropods and Mollusca.

5. Body Segmentation
Division of body parts into segments 

a. Asegmented body: Body is not divisible into segments. For example Chordates.

b. Segmented body: Body is divisible into numbers of linear segments. For example: annelids.

[There are others important biological terms as well. The notes on above heading are on the basis of NEB present syllabus. One can develop their own note as per their easiness. Hope this will help you. HAPPY READING]