Jam tomorrow
Definition 1 of 1
Pro Tip 1/3Empty Promises
Understanding 'jam tomorrow' means recognizing unfulfilled promises or teasers of future rewards that may never come. 
Every meeting, our boss offers 'jam tomorrow' but hasn't improved our working conditions.
Pro Tip 2/3Skepticism Conveyed
'Jam tomorrow' often implies skepticism towards the promised rewards or doubts about the promiser's honesty. 
The developer's promised features are always 'jam tomorrow'; I'll believe it when I see it.
Pro Tip 3/3Metaphorical Use
The phrase doesn't involve actual jam but is a metaphor for any enticing reward promised in the future. 
Mum said we could get a puppy next year, but I suspect it's just 'jam tomorrow'.