An array is a data structure that stores a collection of data items of the same type in a contiguous block of memory. It allows efficient access of elements using an index. One-dimensional arrays represent data as a linear list using a single index. Arrays simplify processing similar data by allowing batch operations. Pseudocode is provided to input student names and marks into arrays, calculate totals and averages, find the highest scoring student, calculate the average of user-input numbers using a loop, swap the first and last elements of an array, and find the largest and smallest elements in an array.