Salary sacrifice is an arrangement with your employer to forego part of your salary or wages in return for your employer providing benefits of a similar value. The sacrificed component of your total salary package is not counted as assessable income for tax purposes, however it will be taxed in your super fund at 15% (which can be less depending on your current marginal tax rate).
Just note that not every employer allows salary sacrificing and some might count your salary sacrifice as part of their obligations to pay Super Guarantee of 9.5% of your ordinary time earnings. It's worth checking this out before entering into an arrangement.
Contributions splitting with your spouse
You can ask your super fund to transfer up to 85% of a financial year’s ‘taxed splittable contributions’ to your spouse. These are generally:
any contributions your employer made for you (your 'before-tax contributions'), including any salary sacrifice contributions; or
any personal contributions you made for yourself that you have advised your super fund you will claim as a tax deduction
It's a good idea to talk to your current superannuation fund to see if they offer contribution splitting - they should be able to help you with the process, but both you and your spouse will need to be members of the same superannuation fund.
There are many finanical considerations to think about here, and in some circumstances it might be better to claim the spouse contributions tax offset using 'after-tax' money (i.e. what you receive in your pay) or even to claim a personal super contributions deduction (if eligible) and then split these contributions. You may benefit from contacting your fund, registered tax professional or a financial advisor depending on how complex your personal financial affairs are.