<?php
$args = array(
'post_type' => 'post',
'posts_per_page' => -1, //show all posts
'tax_query' => array(
array(
'taxonomy' => 'category',
'field' => 'slug',
'terms' => $term->slug,
)
)
);
$posts = new WP_Query($args);
if( $posts->have_posts() ): while( $posts->have_posts() ) : $posts->the_post(); ?>
<?php if(has_post_thumbnail()) { ?>
<?php the_post_thumbnail(); ?>
<?php }
/* no post image so show a default img */
else { ?>
<img src="<?php bloginfo('template_url'); ?>/assets/img/default-img.png" alt="<?php echo get_the_title(); ?>" title="<?php echo get_the_title(); ?>" width="110" height="110" />
<?php } ?>
<?php echo get_the_title(); ?>
<?php the_excerpt(); ?>
<?php endwhile; endif; ?>
https://wordimpress.com/loop-through-categories-and-display-posts-within/