What is the name of a verse consisting of 7 syllables?

In English poetry, the meter is not determined solely by the number of syllables, except in haiku (a form borrowed from another language), so we don't have a word that people use for all lines of verse with seven syllables. Other languages, like French, count syllables in most forms of poetry. The reason is that English is a stress-timed language, and French is a syllable-timed language. This means that in English, the number of stressed syllables in a line is generally more important than the total number of syllables.

Seven-syllable lines in English verse can have several different names.

If you're trying to figure out the meter of a poem like Shakespeare's witches' chants, whose lines have the same pattern of stresses as your example:

Fillet of a fenny snake,
In the cauldron boil and bake;
Eye of newt and toe of frog,
Wool of bat and tongue of dog,
Adder's fork and blind-worm's sting,
Lizard's leg and howlet's wing,

this would be called catalectic trochaic tetrameter. (Catalectic because, compared with regular trochaic tetrameter, all the lines are missing a syllable at the end.)

On the other hand, the exact same pattern of stresses appears in the first line of Hughes Mearnes poem Antigonish:

Yesterday, upon the stair,
I met a man who wasn’t there
He wasn’t there again today
I wish, I wish he’d go away.

And here, it would be classified as headless iambic tetrameter, because the other lines are all iambic tetrameter.

You can also have seven-syllable lines in iambic trimeter, for example the odd-numbered lines of Housman's poem When I was One-and-Twenty, the first verse of which goes:

When I was one-and-twenty
I heard a wise man say,
"Give crowns and pounds and guineas
But not your heart away;
Give pearls away and rubies
But keep your fancy free.”
But I was one-and-twenty,
No use to talk to me.

These lines would be called iambic trimeter with a feminine ending.

Occasionally, English poets have experimented with syllabic verse in English, where the number of syllables in each line is constant. For example, Dylan Thomas's poem In my Craft or Sullen Art, which starts:

In my craft or sullen art
Exercised in the still night
When only the moon rages
And the lovers lie abed
With all their griefs in their arms,

There is actually a word in English for lines of poetry with seven syllables, a "heptasyllable". This word is borrowed from French, and is generally only used in analyses of poetry in languages like French, Spanish, and Italian. I can't even find an analysis of Dylan Thomas's poem above where somebody has used it.