That is a tongue tie.
Two of my children had/ have quite tight tongue ties. Eldest was born in England and hers wasn't spotted until she was a few months old, by which time she was thriving and fully breastfed and although she did gulp air she was putting on weight so well it wasn't considered worth doing anything by then, when it would have been a bigger deal.
Second child was born in Germany and his tongue tie was spotted immediately at the paediatrician check in hospital. I elected to leave it be because it caused dc1 no problems. I'm ambivalent now about whether that was the right decision.
The only problem their tongue ties ever caused was in the early stages of breastfeeding - both got plenty of milk (but I have oversupply and fast let down when breastfeeding so they didn't need a perfect latch) but both were "happy pukers" as someone put it and swallowed air and brought a lot of milk back up.
Both tongue tie children have always had very clear speech for whatever age they are at the time and have never had any problems with eating or breathing.
The dentist brought up the issue of their tongue ties six months ago and said in the very long term it can cause problems with teeth, because your tongue doesn't perform its usual function.
Both dc1 and dc2 (now ages 12 nearly 13 and 14 nearly 15) had an assessment with a craniofacial surgeon in November.
What a lot of people don't know is that cutting tongue ties becomes an incredibly simple, quick procedure in older children and adults.
However the surgeon said it's not necessary to cut the tongue ties and debatable whether there's any need. He said his own son has a tongue tie which he elected to leave alone. He said even in tiny babies there is a small risk to cutting a tongue tie and "do no harm" is his guiding principle if the child is not experiencing problems.
He was willing to cut the tongue ties if the children wanted them cut, not if not.
Cutting tongue ties is only a big deal requiring general anaesthesia in older babies and small children who cannot keep their head absolutely and completely still for five minutes when necessary.
My eldest had her tongue tie cut at her own request; she said it was annoying. My second child chose not to, but the surgeon said he can come back in a few years if he changes his mind.
Dc1 said having the tongue tie cut was less unpleasant than having a baby tooth removed to encourage the tooth behind to come through in the right place. It took less than 5 minutes with a local anesthetic.
She had some discomfort in the evening but has had no ill effects and her worry about having to learn to use her new "free" tongue was unfounded, her speech remains clear, exactly as it has always been.
So she can always get it done later if she wants.
In all honesty I'd adopt a wait and see approach at ten months, as she's too old for the newborn procedure and would need general anaesthesia at that age. As you've breastfed successfully it may cause no problems.
DC2s tongue tie is so tight the dentist asked if he could take photos of it for a paper he's writing for a professional journal! Yet it's caused no problems since the breastfeeding stage.