The American Heritage® Dictionary of the English Language, 4th edition Copyright © 2010 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
transitive verb de·fo·cused or de·fo·cussed, de·fo·cus·ing or de·fo·cus·sing, de·fo·cus·es or de·fo·cus·ses
To cause (a beam or a lens) to deviate from accurate focus.noun
The act or result of causing a lens to deviate from accurate focus.