Ah, I’m sorry. Let me explain.
Instead of singing pitches or playing an instrument, I sing the solfege equivalent. For example, if you were humming the melody to “Mary had a Little Lamb”, I would chime in with the appropriate solfege syllables that match the melody, namely:
“Mi re do re mi mi mi, re re re, mi sol sol. Mi re do re mi mi mi mi re re mi re do.”
There are also hand signals that follow along with each pitch. Think of it as the scene in The Sound of Music, where Maria begins to teach the children to sing.
Do - a deer, a female deer
Re - a drop of golden sun…
The entire thing sounds preposterous (and a wee bit childish), doesn’t it? But here’s where the benefits come into play. Because while you are singing the note in question, you are also verbally pronouncing a syllable and forming a sign with your hands. Your brain will immediately intervene if you accidentally mix them up for whatever reason. This layer of redundancy is excellent for training your ear and extending pitch memory, once you get more proficient at it.
With enough diligent practice, solfege works to maintain your pitch accuracy as well. It’s easy for the human voice to falter and flatten, especially at the high range, but with the extra “layer” of solfege underneath, your brain will instinctively realize that you aren’t singing quite the right pitch, and compensate for it.
There is so much more I could ramble on about, but suffice it to say, when I say “I solfege”, I mean to say “I practice singing”, but with these special syllables - Do, re, mi, fa, sol, la, and ti.
Addendum:
Because Solfege is more of a skill as opposed to “knowledge”, it is much much easier for young children to learn it. This is why the Kodaly method focuses on solfege as a means to teach children the basics of music. After a month, a child will be so proficient that you need only raise your hand in a sign, and they will sing the appropriate pitch, once given a tonic.
Not to say that there’s no point now that we’re older! I began learning solfege when I was 20, and after one year, I was proficient enough to hear, sing, and interpret solfege on the fly.