Within HRPA's Job Design content, job enlargement is defined as the horizontal expansion of a job---adding a greater number and variety of tasks at the same level of responsibility. By contrast, job enrichment increases depth (autonomy, responsibility, decision authority), job sharing divides one full-time job between two people, and job grading/classification groups jobs into classes for pay structure purposes rather than changing task content.

Relevant HRPA references (no external links):

HRPA Study Guide -- Organizational Effectiveness: Job Design (job enlargement vs. enrichment), Job Sharing, Job Classification.

HRPA Competency Framework -- Organizational Effectiveness: design and redesign of jobs to improve efficiency and motivation.