With the 7-row to 6-row transition in 2012, the standard ThinkPad keyboard lost some keys - to be exact, the new layout has 5 keys less. The functions assigned to these keys were mostly legacy functions most people don´t use and are only needed for very specific tasks, like scroll-lock, system-request, break or pause. Also the menu key.
What you may not know however: These functions still exist, even though their names are not printed on the keys they are now assigned for. Therefore, they are hidden functions now.
On Ivy-Bridge, Haswell and Broadwell ThinkPads, and propably future generations with the same layout as well, these hidden functions are:
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Fn + B: Break
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Fn + K: ScrLK
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Fn + P: Pause
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Fn + S: SysRq
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FN + 4: Standby
The Fn + 4 function was actually added later on the Haswell models with a BIOS update (propably due to customer demand), so don´t wonder if this function doesn´t work on an early Haswell or an Ivy-Bridge ThinkPad.