| LDF | Lying Down Fit | - | NASA |
| LFTWM | Looking For 3 Wise Men (applied To Young Pregnant Females Who Deny Having Had Intercourse) | - | NASA |
| LGFD | Looks Good From Door (but Not Closely Examined) | - | NASA |
| LGFTC | Looks Good From The Corridor (but Not Closely Examined) | - | NASA |
| LMC | Low Marble Count (low IQ) | - | NASA |
| LOBNH | Lights On But Nobody Home | - | NASA |
| LOFD | Looks Okay From Door | - | NASA |
| LOL | Little Old Lady | - | NASA |
| LOLFDGB | Little Old Lady, Fall Down, Go Boom | - | NASA |
| LOLINAD | Little Old Lady In No Acute Distress | - | NASA |
| LOLITS | (US) Little Old Lady In Tennis Shoes (60+ Years-old); (UK) Little Old Lady In Twin-Set (50-60+ Years-old) | - | NASA |
| LPT | Low Pain Threshold | - | NASA |
| LRO | Luck Ran Out (cheated Death Before, But Not This Time) | - | NASA |
| LT | Lantern Test - Shine A Torch In The Subject's Mouth And The Eyes Light Up (no Brain) | - | NASA |
| LWS | (US) Low Wallet Syndrome (No Medical Insurance Or Money) | - | NASA |
