Babar,

Its an old saying. Picture sitting down at a table with many people squeezed closely together or a modern situatuation would be sitting in an airline seat. Your elbows are pressed against your ribs and it makes normal operation of your arms constricted. Like eating a meal in an airline seat or eating at a crowded table.

Having "elbow room" describes a custom of holding ones elbows out at 45 degrees from vertical, to ensure your have enough room on either side to avoid bumping into your neighbors as you operate your arms (as in eating at a table or whatever).

Used in circuitry, the phrase usually means you have reserve capacity in your design to handle the unexpected. A microprocessor with no spare I/O pins and/or no spare processing time would be an example of one that is confined and hence lacking in "elbow room".

-Jay C. Box