Understanding projection layer for BLSTM
A &quot;projection&quot; is a simple linear/dense layer, that is, a matrix multiplication and a bias vector addition.
It is called projection because you &quot;project&quot; a representation of dimensionality $M$ into a representation space of dimensionality $N$.
Sometimes, especially for sequences or 2D data, these projections are implemented as a convolution of size 1, which is equivalent to the computations I described above.