Global aphantasia is a complete absence of voluntary imagery across every sense, sometimes called total aphantasia. It can be congenital or acquired.
Zeman · Neuropsychologia
Ten years after aphantasia was named, Adam Zeman argues it likely has several subtypes and that most abilities are spared, with memory for one's own past differing most. He urges an open mind in this young field.
Zeman and colleagues · Cortex
This short definition, published in a special issue of the journal Cortex, describes aphantasia as the absence or near-absence of imagery, most often the inability to picture things while fully awake, as opposed to simply thinking about them. Aphantasia affects deliberate imagery, may affect spontaneous imagery, and often leaves imagery in dreams intact. It can be lifelong or acquired, and the note proposes labels such as visual, auditory, multisensory and global aphantasia, while recording that some researchers keep the word for vision alone.
Monzel and colleagues · Cortex
In a short reply within a debate over names, the authors argue for keeping one term, aphantasia, for absent or markedly reduced voluntary imagery in any sense, with a word added for the sense involved, such as visual or auditory aphantasia, or multisensory aphantasia when all senses are affected. They describe hyperphantasia as the opposite: imagery said to rival real perception. They note that many people with aphantasia report rare spontaneous flashes of imagery or imagery in dreams, and that lacking imagery does not mean lacking imagination.