These initials indicate LOW SMOKE + O (Zero) HALOGENS:

– LOW SMOKE. To the following standards referred:

EN 61034: Measurement of smoke density of cables burning under defined conditions. IEC 61034 also.

So Low Smoke means low opacity of smoke emitted.

– O (Zero) HALOGEN. To the following standards referred:

EN 50267: Common test methods for cables under fire conditions. Test on gases evolved during combustion of materials from cables. Determination of the amount of halogen acid gas. IEC 60754 also.

So Zero Halogens mean no acid gases emitted by the combustion.

To know more about the most used acronyms cabling: CABLING ACRONYMS