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What glue is it? Is it safe for attaching?
Its probably an RTV Silicone like Silastic. It comes in various forms but RTV Silicone is the generic name.
The connection is first soldered and then basically any glue that is very viscous can be used ie it does not flow.
It is there to provide support to the wire and board so the soldered connection does not fail.
Required, but never shown