I have always used the terms synonymously but I think there is technically a different between the two.
For example, given two seemingly similar assets, one is classified a security and the other a fund:
╔═══════╦════════════════════╦═══════════╦══════════╦════════════════╗
║ Asset ║ Description ║ Type ║ Holdings ║ Classification ║
╠═══════╬════════════════════╬═══════════╬══════════╬════════════════╣
║ ZAG ║ BMO Aggregate Bond ║ Index ETF ║ 1203 ║ FI Security ║
║ ZDB ║ BMO Discount ║ Index ETF ║ 261 ║ FI Fund ║
╚═══════╩════════════════════╩═══════════╩══════════╩════════════════╝