The term interior has many connotations and usually referred to any space inside a building whether it is a magnificent theatre or a small apartment. In other words it is the space available within the masonry walls of a building for the use of the specific purpose for which it is intended.
The space consists of three dimensions viz the length breadth and the height of the place. The interior design of a space is dependent on the purpose and use of the space for which it s intended. For example the height of a cinema hall or opera theatre may be comparatively larger than that of the height of school building or the space intended for an office. Similarly the same height of a bed room in your house or the store room may be still less since the purpose is different.
The interior decoration refers not to the structure of the building or to its three dimensional aspects alone but to the general ambience of the space, including the space , furniture, decorative, and other utilities occupying the space. Again the utility of the space and the articles and other items decorating the room depends on the perception of the individual or the individuals occupying the space. A simple example would be while no sensible person like to see his Bed or Office room cluttered none of us give that much importance to the store room with respect to the free space orthe order in the store room , though it is always better to be organized every where. Similarly the space that is considered to be useless by you may be the best suited for the children to use when they play a hide and seek game. Hence it is the use and the view point that matters.
Let us take an example of a typical bed room. A typical bedroom contains the built in comforts like cupboards and other architectural elements and the additional utilities added by the occupant. Further the bed room is also a part of the entire house plan and not a space in isolation. The bed room may have the built in architectural elements like the balcony, the attached bath or some times the attached study room etc all of which has a supplementary role in a bed room. The additional or imposed elements like the double bed, wardrobe, the table, book shelf or T.V. rack and the Lamps also add to the interior beauty and convenience of the room. There need to be a perfect balance and harmony among all these elements else it would defeat the very purpose of a comfortable bed room. It is also a matter of importance to maintain a balance between the furnished space and the free space since it is the free space that contributes to the aesthetic look and the comfort of movement inside the room. The free space of the room may be well compared to the background of a beautiful painting that projects the painting itself.
It is the combined creative talents of the architect , the decorator and the designer that make the real difference in a space irrespective of the purpose for which it is being used. You can read more on home interior decorating here