An infix is an affix inserted inside a word stem (an existing word). It contrasts with adfix, a rare term for an affix attached to the outside of a stem, such as a prefix or suffix.
When marking text for interlinear glossing, most affixes are separated with a hyphen, but infixes are separated with ⟨angle brackets⟩.
English has almost no true infixes (as opposed to tmesis), and those it does have are marginal. A few are heard in colloquial speech, and a few more are found in technical terminology.
None of the following are recognized in standard English.
Up drove the Hearse, Caddillac
A crowd of people gathered round it all dressed in black
And as they removed her body from the car
Such pain I never knew, did fill my hear
I lost the only one I've ever loved
The Lord has returned up above
Life will never be the same again
It was the beginning of my end
It happened on a Saturday night
My love and I had just had a silly fight
She got into her car and angrily drove away
Neither of us knew then, that she would never see another day
What have I done Lord to deserve this misery
all my life and all my world have come falling down on me end
I was a home watching my TV
When the noise of the phone rudely disturbed me
I wasn't too sure at first, just what the doctor meant
When he informed me that there had been an accident
Why, oh why, I heard her mother cry
As I rushe to the scene with the tears in my eyes
Somebody asked, somebody asked who was the next of kin