(N/A) $\rightarrow$ Classification is not a single-step process but involves a hierarchy of steps in which each step represents a taxonomic rank.
$\rightarrow$ Each category,referred to as a unit of classification,represents a rank and is commonly termed as a $taxon$ (plural: $taxa$).
$\rightarrow$ Taxonomic categories and hierarchy can be illustrated by an example.
$\rightarrow$ Insects represent a group of organisms sharing common features like three pairs of jointed legs.
$\rightarrow$ This means insects are recognizable concrete objects which can be classified and thus were given a rank or category.
$\rightarrow$ Groups represent a category and further denote a rank.
$\rightarrow$ Each rank or $taxon$ represents a unit of classification.
$\rightarrow$ These taxonomic groups/categories are distinct biological entities and not merely morphological aggregates.
$\rightarrow$ Taxonomical studies of all known organisms have led to the development of common categories.
$\rightarrow$ All organisms,including those in plant and animal kingdoms,have $species$ as the lowest category.
$\rightarrow$ To place an organism in various categories,the basic requirement is the knowledge of characters.
$\rightarrow$ This helps in identifying similarities and dissimilarities among the individuals of the same kind of organisms as well as of other kinds of organisms.