what is the "less than followed by dash" operator in go language?

You've already got answers, but here goes.

Think of a channel as a message queue.

If the channel is on the right of the left arrow (<-) operator, it means to dequeue an entry. Saving the entry in a variable is optional

e <- q

If the channel is on the left of the left arrow operator, it means to enqueue an entry.

q <- e

Further note about "dequeue" (receive) without storing in a variable: it can be used on a non-buffered queue to implement something like a "wait/notify" operation in Java: One coroutine is blocked waiting to dequeue/receive a signal, then another coroutine enqueues/sends that signal, the content of which is unimportant. (alternately, the sender could be blocked until the receiver pulls out the message)

<- is used in more than one place in the language specification:

Channel types:

The <- operator specifies the channel direction, send or receive. If no direction is given, the channel is bi-directional. A channel may be constrained only to send or only to receive by conversion or assignment.

Receive operator:

For an operand ch of channel type, the value of the receive operation <-ch is the value received from the channel ch. The type of the value is the element type of the channel. The expression blocks until a value is available. Receiving from a nil channel blocks forever. Receiving from a closed channel always succeeds, immediately returning the element type's zero value.

Send statements:

A send statement sends a value on a channel. The channel expression must be of channel type and the type of the value must be assignable to the channel's element type.

SendStmt = Channel "<-" Expression .
Channel  = Expression .

The receive operator is also a fundamental part of the select statement

Receive operator

For an operand ch of channel type, the value of the receive operation <-ch is the value received from the channel ch.

It receives a value from a channel. See http://golang.org/ref/spec#Receive_operator