1. A solid is a state of matter characterized by particles arranged such that their shape and volume are relatively stable. The constituents of a solid tend to be packed together much closer than the particles in a gas or liquid. The reason a solid has a rigid shape is that the atoms or molecules are tightly connected via chemical bonds. The bonding may produce either a regular lattice (as seen in ice, metals, and crystals) or an amorphous shape (as seen in glass or amorphous carbon). A solid is one of the four fundamental states of matter, along with liquids, gases, and plasma.

2. Crystalline solids have regular ordered arrays of components held together by uniform intermolecular forces, whereas the components of amorphous solids are not arranged in regular arrays.

3. IONIC SOLIDS - DEFINITION
Ionic Solids are solids composed of oppositely charged ions. They consist of positively charged cations and negatively charged anions .When Ionic Solids are dissolved in water the cations and the anions separate, they become free to move in the water allowing the solution to conduct electrical current. e.g NaCl, ZnS

MOLECULAR SOLIDS - 

DEFINITION
A molecular solid is a solid composed of molecules held together by the van der Waals forces. Because these dipole forces are weaker than covalent or ionic bonds, molecular solids are soft and have relatively low melting temperature.
There are three types of molecular solids:
Non-polar molecular solids
Polar molecular solids
Hydrogen-bonded molecular solids. Examples are HCl, F, O, N

CHARACTERISTICS OF NON-POLAR MOLECULAR SOLIDS - 

DEFINITION
The crystalline solids in which the constituent particles are either atoms like those of noble gases or non-polar molecules.The force holding molecules are vanderwaal forces.

The main characteristics are:
They are non-conductors of electricity
They are generally soft
They have low melting and boiling point
Examples are H₂ ,Cl₂