Summer: Time to preserve fruit. Time to travel. Time for music. Jams everywhere!
Jam is a sweet spread made from the pulp and juice of fruit cooked with sugar and pectin. There’s strawberry jam, apricot jam, raspberry jam … you name it.
Jelly is only made from the juice of fruit; it’s clear and doesn’t contain any chunks or pulp.
For preserves, the fruit is cut into pieces or used entire and cooked with sugar.
Please note:
It’s only called marmalade when it’s made from citrus fruits, such as oranges or lemons. With any other fruit, it’s jam.
A jam in general is a block or congestion.
During rush hour, or at the beginning and the end of the holidays, a lot of cars block the roads and streets, forming a traffic jam.
And who has never rolled up their sleeves to fix a paper jam in a photocopier, or despaired over one in their printer?
In music, especially in jazz or rock, a jam session is a spontaneous or informal 
music event.
Musicians who don’t normally perform together play for their own enjoyment in an unrehearsed performance with improvised solos or variations of tunes they all know.
As a verb, jam can mean
• to squeeze or pack something tightly into something
We jammed the suitcases into the car boot as best as we could.
During rush hour, commuters are jammed into the trains.
• to push something using a lot of force
He jammed his hat on and stormed out.
She saw a child running onto the street and jammed on the brakes.
• to block (a mechanism), to get stuck and be unable to move
She couldn’t shoot because her gun had jammed.
My key jammed in the lock, and I couldn’t open the door.
A stone had jammed the engine and ruined it.
• to play music spontaneously with a group of people
They all jammed together for a couple of minutes at the end of the concert.
And here are three jam idioms for you:
• to be in a jam means to be in a difficult situation.
I’m in a jam – I’ve lost my wallet!
• jam tomorrow is something good that is always promised but never comes
Stop promising me jam tomorrow; I don’t believe you anymore.
• jam on it / jam on top – to say that someone should be grateful for what they got, and not demand even more
What more do you want – jam on it?
You want it all and jam on top, right?
What’s your favourite kind of jam? Mine is the strawberry jam my parents make every summer – it’s just SO delicious!